]> git.saurik.com Git - apple/ld64.git/blobdiff - src/ld.cpp
ld64-77.1.tar.gz
[apple/ld64.git] / src / ld.cpp
index 3b6805946e9c1fc9061e809bb97369965179de4c..a2a56b9d538548cfd2cd6d8c0d90aca11d4e678d 100644 (file)
@@ -1,16 +1,15 @@
-/* -*- mode: C++; c-basic-offset: 4; tab-width: 4 -*- 
- *
- * Copyright (c) 2005 Apple Computer, Inc. All rights reserved.
+/* -*- mode: C++; c-basic-offset: 4; tab-width: 4 -*-*
+ * Copyright (c) 2005-2007 Apple Inc. All rights reserved.
  *
  * @APPLE_LICENSE_HEADER_START@
- * 
+ *
  * This file contains Original Code and/or Modifications of Original Code
  * as defined in and that are subject to the Apple Public Source License
  * Version 2.0 (the 'License'). You may not use this file except in
  * compliance with the License. Please obtain a copy of the License at
  * http://www.opensource.apple.com/apsl/ and read it before using this
  * file.
- * 
+ *
  * The Original Code and all software distributed under the License are
  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  * Please see the License for the specific language governing rights and
  * limitations under the License.
- * 
+ *
  * @APPLE_LICENSE_HEADER_END@
  */
 #include <stdlib.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/mman.h>
+#include <sys/sysctl.h>
 #include <fcntl.h>
 #include <errno.h>
-#include <mach-o/loader.h>
+#include <limits.h>
+#include <unistd.h>
+#include <mach/mach_time.h>
+#include <mach/vm_statistics.h>
+#include <mach/mach_init.h>
+#include <mach/mach_host.h>
 #include <mach-o/fat.h>
+#include <dlfcn.h>
 
 #include <string>
+#include <map>
 #include <set>
 #include <string>
 #include <vector>
 #include <list>
 #include <algorithm>
 #include <ext/hash_map>
+#include <dlfcn.h>
+#include <AvailabilityMacros.h>
 
 #include "Options.h"
 
 #include "ObjectFile.h"
-#include "ObjectFileMachO-all.h"
 
-#include "ExecutableFile.h"
-#include "ExecutableFileMachO-all.h"
+#include "MachOReaderRelocatable.hpp"
+#include "MachOReaderArchive.hpp"
+#include "MachOReaderDylib.hpp"
+#include "MachOWriterExecutable.hpp"
 
-#include "SectCreate.h"
+#define LLVM_SUPPORT 0
+#if LLVM_SUPPORT
+#include "LLVMReader.hpp"
+#endif
 
-#if 0
-static void dumpAtom(ObjectFile::Atom* atom)
-{
-       //printf("atom:    %p\n", atom);
-       
-       // name
-       printf("name:    %s\n",  atom->getDisplayName());
-       
-       // scope
-       switch ( atom->getScope() ) {
-               case ObjectFile::Atom::scopeTranslationUnit:
-                       printf("scope:   translation unit\n");
-                       break;
-               case ObjectFile::Atom::scopeLinkageUnit:
-                       printf("scope:   linkage unit\n");
-                       break;
-               case ObjectFile::Atom::scopeGlobal:
-                       printf("scope:   global\n");
-                       break;
-               default:
-                       printf("scope:   unknown\n");
-       }
-       
-       // segment and section
-       printf("section: %s,%s\n", atom->getSegment().getName(), atom->getSectionName());
-
-       // attributes
-       printf("attrs:   ");
-       if ( atom->isTentativekDefinition() )
-               printf("tentative ");
-       else if ( atom->isWeakDefinition() )
-               printf("weak ");
-       if ( atom->isCoalesableByName() )
-               printf("coalesce-by-name ");
-       if ( atom->isCoalesableByValue() )
-               printf("coalesce-by-value ");
-       if ( atom->dontDeadStrip() )
-               printf("dont-dead-strip ");
-       if ( atom->isZeroFill() )
-               printf("zero-fill ");
-       printf("\n");
-       
-       // size
-       printf("size:    0x%012llX\n", atom->getSize());
-       
-       // content
-       uint8_t content[atom->getSize()];
-       atom->copyRawContent(content);
-       printf("content: ");
-       if ( strcmp(atom->getSectionName(), "__cstring") == 0 ) {
-               printf("\"%s\"", content);
-       }
-       else {
-               for (unsigned int i=0; i < sizeof(content); ++i)
-                       printf("%02X ", content[i]);
-       }
-       printf("\n");
-       
-       // references
-       std::vector<ObjectFile::Reference*>&  references = atom->getReferences();
-       const int refCount = references.size();
-       printf("references: (%u)\n", refCount);
-       for (int i=0; i < refCount; ++i) {
-               ObjectFile::Reference* ref = references[i];
-               printf("   %s\n", ref->getDescription());
-       }
-       
-       // attributes
-       
-}
+#include "OpaqueSection.hpp"
 
-#endif
 
 class CStringComparor
 {
@@ -138,7 +82,7 @@ class Section : public ObjectFile::Section
 public:
        static Section* find(const char* sectionName, const char* segmentName, bool zeroFill);
        static void             assignIndexes();
-
+       const char*             getName() { return fSectionName; }
 private:
                                        Section(const char* sectionName, const char* segmentName, bool zeroFill);
 
@@ -147,6 +91,7 @@ private:
                bool operator()(Section* left, Section* right);
        };
 
+       typedef __gnu_cxx::hash_map<const char*, uint32_t, __gnu_cxx::hash<const char*>, CStringEquals> NameToOrdinal;
        typedef __gnu_cxx::hash_map<const char*, class Section*, __gnu_cxx::hash<const char*>, CStringEquals> NameToSection;
        //typedef std::map<const char*, class Section*, CStringComparor> NameToSection;
 
@@ -156,26 +101,22 @@ private:
 
        static NameToSection                    fgMapping;
        static std::vector<Section*>    fgSections;
+       static NameToOrdinal                    fgSegmentDiscoverOrder;
 };
 
 Section::NameToSection Section::fgMapping;
 std::vector<Section*>  Section::fgSections;
+Section::NameToOrdinal Section::fgSegmentDiscoverOrder;
 
 Section::Section(const char* sectionName, const char* segmentName, bool zeroFill)
  : fSectionName(sectionName), fSegmentName(segmentName), fZeroFill(zeroFill)
 {
-       //fprintf(stderr, "new Section(%s, %s)\n", sectionName, segmentName);
+       this->fIndex = fgSections.size();
+       //fprintf(stderr, "new Section(%s, %s) => %p, %u\n", sectionName, segmentName, this, this->getIndex());
 }
 
 Section* Section::find(const char* sectionName, const char* segmentName, bool zeroFill)
 {
-#if 0
-       std::pair<NameToSection::iterator, NameToSection::iterator> range = fgMapping.equal_range(sectionName);
-       for (NameToSection::iterator it=range.first; it != range.second; it++) {
-               if ( strcmp(it->second->fSegmentName, segmentName) == 0 )
-                       return it->second;
-       }
-#endif
        NameToSection::iterator pos = fgMapping.find(sectionName);
        if ( pos != fgMapping.end() ) {
                if ( strcmp(pos->second->fSegmentName, segmentName) == 0 )
@@ -186,12 +127,21 @@ Section* Section::find(const char* sectionName, const char* segmentName, bool ze
                                return *it;
                }
        }
-       
+
        // does not exist, so make a new one
        Section* sect = new Section(sectionName, segmentName, zeroFill);
-       sect->fIndex = fgMapping.size();
        fgMapping[sectionName] = sect;
        fgSections.push_back(sect);
+
+       if ( (strcmp(sectionName, "__text") == 0) && (strcmp(segmentName, "__TEXT") == 0) ) {
+               // special case __textcoal_nt to be right after __text
+               find("__textcoal_nt", "__TEXT", false);
+       }
+
+       // remember segment discovery order
+       if ( fgSegmentDiscoverOrder.find(segmentName) == fgSegmentDiscoverOrder.end() ) 
+               fgSegmentDiscoverOrder[segmentName] = fgSegmentDiscoverOrder.size();
+
        return sect;
 }
 
@@ -205,29 +155,24 @@ int Section::Sorter::segmentOrdinal(const char* segName)
                return 3;
        if ( strcmp(segName, "__OBJC") == 0 )
                return 4;
+       if ( strcmp(segName, "__OBJC2") == 0 )
+               return 5;
        if ( strcmp(segName, "__LINKEDIT") == 0 )
                return INT_MAX; // linkedit segment should always sort last
-       else 
-               return 5;
+       else
+               return fgSegmentDiscoverOrder[segName]+6;
 }
 
 
 bool Section::Sorter::operator()(Section* left, Section* right)
 {
        // Segment is primary sort key
-       const char* leftSegName = left->fSegmentName;
-       const char* rightSegName = right->fSegmentName;
-       int segNameCmp = strcmp(leftSegName, rightSegName);
-       if ( segNameCmp != 0 )
-       {
-               int leftSegOrdinal = segmentOrdinal(leftSegName);
-               int rightSegOrdinal = segmentOrdinal(rightSegName);
-               if ( leftSegOrdinal < rightSegOrdinal )
-                       return true;
-               if ( leftSegOrdinal == rightSegOrdinal )
-                       return segNameCmp < 0;
+       int leftSegOrdinal = segmentOrdinal(left->fSegmentName);
+       int rightSegOrdinal = segmentOrdinal(right->fSegmentName);
+       if ( leftSegOrdinal < rightSegOrdinal )
+               return true;
+       if ( leftSegOrdinal > rightSegOrdinal )
                return false;
-       }
 
        // zerofill section sort to the end
        if ( !left->fZeroFill && right->fZeroFill )
@@ -240,59 +185,103 @@ bool Section::Sorter::operator()(Section* left, Section* right)
 }
 
 void Section::assignIndexes()
-{
-       //printf("unsorted:\n");
+{      
+       //printf("unsorted sections:\n");
        //for (std::vector<Section*>::iterator it=fgSections.begin(); it != fgSections.end(); it++) {
        //      printf("section: name=%s, segment: name=%s, discovery order=%d\n", (*it)->fSectionName, (*it)->fSegmentName, (*it)->fIndex);
        //}
 
        // sort it
        std::sort(fgSections.begin(), fgSections.end(), Section::Sorter());
-       
+
        // assign correct section ordering to each Section object
        unsigned int newOrder = 1;
-       for (std::vector<Section*>::iterator it=fgSections.begin(); it != fgSections.end(); it++) 
+       for (std::vector<Section*>::iterator it=fgSections.begin(); it != fgSections.end(); it++)
                (*it)->fIndex = newOrder++;
 
-       //printf("sorted:\n");
+       //printf("sorted sections:\n");
        //for (std::vector<Section*>::iterator it=fgSections.begin(); it != fgSections.end(); it++) {
-       //      printf("section: name=%s\n", (*it)->fSectionName);
+       //      printf("section: index=%d, obj=%p, name=%s\n", (*it)->fIndex, (*it), (*it)->fSectionName);
        //}
 }
 
-class Linker {
+class Linker : public ObjectFile::Reader::DylibHander {
 public:
                                                Linker(int argc, const char* argv[]);
 
+       const char*                     getArchPrefix();
+       const char*                     architectureName();
+       bool                            showArchitectureInErrors();
+       bool                            isInferredArchitecture();
        void                            createReaders();
        void                            createWriter();
-       void                            addInputFile(ObjectFile::Reader* reader);
+       void                            addInputFile(ObjectFile::Reader* reader, const Options::FileInfo& );
        void                            setOutputFile(ExecutableFile::Writer* writer);
        void                            link();
+       void                            optimize();
        
-       
+       // implemenation from ObjectFile::Reader::DylibHander
+       virtual ObjectFile::Reader* findDylib(const char* installPath, const char* fromPath);
+
 private:
+       struct WhyLiveBackChain
+       {
+               WhyLiveBackChain*       previous;
+               const char*                     name;
+       };
+
        ObjectFile::Reader*     createReader(const Options::FileInfo&);
        void                            addAtom(ObjectFile::Atom& atom);
        void                            addAtoms(std::vector<class ObjectFile::Atom*>& atoms);
        void                            buildAtomList();
+       void                            processDylibs();
+       void                            updateContraints(ObjectFile::Reader* reader);
+       void                            loadAndResolve();
+       void                            processDTrace();
+       void                            checkObjC();
        void                            loadUndefines();
+       void                            checkUndefines();
        void                            addWeakAtomOverrides();
        void                            resolveReferences();
-       void                            deadStrip();
+       void                            deadStripResolve();
+       void                            addLiveRoot(const char* name);
+       ObjectFile::Atom*       findAtom(const Options::OrderedSymbol& pair);
+       void                            logArchive(ObjectFile::Reader* reader);
+       void                            sortSections();
        void                            sortAtoms();
        void                            tweakLayout();
+       void                            writeDotOutput();
+       static bool                     minimizeStab(ObjectFile::Reader::Stab& stab);
+       static const char*      truncateStabString(const char* str);
+       void                            collectDebugInfo();
        void                            writeOutput();
+       ObjectFile::Atom*       entryPoint();
+       ObjectFile::Atom*       dyldHelper();
+       const char*                     assureFullPath(const char* path);
+       void                            markLive(ObjectFile::Atom& atom, Linker::WhyLiveBackChain* previous);
+       void                            collectStabs(ObjectFile::Reader* reader, std::map<const class ObjectFile::Atom*, uint32_t>& atomOrdinals);
+       void                            synthesizeDebugNotes(std::vector<class ObjectFile::Atom*>& allAtomsByReader);
+       void                            printStatistics();
+       void                            printTime(const char* msg, uint64_t partTime, uint64_t totalTime);
+       char*                           commatize(uint64_t in, char* out);
+       void                            getVMInfo(vm_statistics_data_t& info);
+       cpu_type_t                      inferArchitecture();
+       void                            addDtraceProbe(ObjectFile::Atom& atom, uint32_t offsetInAtom, const char* probeName);
+       void                            checkDylibClientRestrictions(ObjectFile::Reader* reader);
+       void                            logDylib(ObjectFile::Reader* reader, bool indirect);
        
-       void                            resolve(ObjectFile::Reference* reference);
-       void                            resolveFrom(ObjectFile::Reference* reference);
-       void                            addJustInTimeAtoms(const char* name);
-       
-       void                            addDylib(ObjectFile::Reader* reader, const Options::FileInfo& info);
-       void                            addIndirectLibraries(ObjectFile::Reader* reader);
-       bool                            haveIndirectLibrary(const char* path, ObjectFile::Reader* reader);
-       bool                            haveDirectLibrary(const char* path);
-       
+       void                                                                    resolve(ObjectFile::Reference* reference);
+       void                                                                    resolveFrom(ObjectFile::Reference* reference);
+       std::vector<class ObjectFile::Atom*>*   addJustInTimeAtoms(const char* name);
+       void                                                                    addJustInTimeAtomsAndMarkLive(const char* name);
+
+       ObjectFile::Reader*     addDylib(ObjectFile::Reader* reader, const Options::FileInfo& info, uint64_t mappedLen);
+       ObjectFile::Reader*     addObject(ObjectFile::Reader* reader, const Options::FileInfo& info, uint64_t mappedLen);
+       ObjectFile::Reader*     addArchive(ObjectFile::Reader* reader, const Options::FileInfo& info, uint64_t mappedLen);
+
+       void                            logTraceInfo(const char* format, ...);
+
+
        class SymbolTable
        {
        public:
@@ -302,52 +291,204 @@ private:
                ObjectFile::Atom*       find(const char* name);
                unsigned int            getRequireCount() { return fRequireCount; }
                void                            getNeededNames(bool andWeakDefintions, std::vector<const char*>& undefines);
+               typedef __gnu_cxx::hash_map<const char*, ObjectFile::Atom*, __gnu_cxx::hash<const char*>, CStringEquals> Mapper;
        private:
-               typedef std::map<const char*, ObjectFile::Atom*, CStringComparor> Mapper;
                Linker&                         fOwner;
                Mapper                          fTable;
                unsigned int            fRequireCount;
        };
-       
-       struct AtomSorter
+
+       class AtomSorter
        {
-               bool operator()(ObjectFile::Atom* left, ObjectFile::Atom* right);
+       public:
+               AtomSorter(std::map<const ObjectFile::Atom*, uint32_t>* map) : fOverriddenOrdinalMap(map) {}
+               bool operator()(const ObjectFile::Atom* left, const ObjectFile::Atom* right);
+       private:
+               std::map<const ObjectFile::Atom*, uint32_t>*    fOverriddenOrdinalMap;
        };
-       
+
        typedef std::map<const char*, uint32_t, CStringComparor> SectionOrder;
-       
+
+       struct DTraceProbeInfo {
+               DTraceProbeInfo(const ObjectFile::Atom* a, uint32_t o, const char* n) : atom(a), offset(o), probeName(n) {}
+               const ObjectFile::Atom*                 atom;
+               uint32_t                                                offset;
+               const char*                                             probeName;
+       };
+       typedef __gnu_cxx::hash_map<const char*, std::vector<DTraceProbeInfo>, __gnu_cxx::hash<const char*>, CStringEquals>     ProviderToProbes;
+       typedef __gnu_cxx::hash_set<const char*, __gnu_cxx::hash<const char*>, CStringEquals>  CStringSet;
+       typedef __gnu_cxx::hash_map<const char*, ObjectFile::Reader*, __gnu_cxx::hash<const char*>, CStringEquals>      InstallNameToReader;
+
        struct IndirectLibrary {
                const char*                                                     path;
                uint64_t                                                        fileLen;
                ObjectFile::Reader*                                     reader;
                std::set<ObjectFile::Reader*>           parents;
-               ObjectFile::Reader*                                     reExportParent;
+               ObjectFile::Reader*                                     reExportedViaDirectLibrary;
        };
-       
+
+       ObjectFile::Reader* findDirectLibraryWhichReExports(struct IndirectLibrary& indirectLib);
+
        Options                                                                                         fOptions;
        SymbolTable                                                                                     fGlobalSymbolTable;
-       unsigned int                                                                            fWeakSymbolsAddedCount;
+       uint32_t                                                                                        fNextInputOrdinal;
        std::vector<class ObjectFile::Reader*>                          fInputFiles;
        ExecutableFile::Writer*                                                         fOutputFile;
-       std::vector<ExecutableFile::DyLibUsed>                          fDynamicLibraries;
-       std::list<IndirectLibrary>                                                      fIndirectDynamicLibraries;
+       InstallNameToReader                                                                     fDylibMap;
+       std::map<ObjectFile::Reader*,DynamicLibraryOptions> fDylibOptionsMap;
+       std::set<ObjectFile::Reader*>                                           fDylibsProcessed;
+       ObjectFile::Reader*                                                                     fBundleLoaderReader;
+       std::vector<class ObjectFile::Reader*>                          fReadersThatHaveSuppliedAtoms;
        std::vector<class ObjectFile::Atom*>                            fAllAtoms;
+       std::set<class ObjectFile::Reader*>                                     fArchiveReaders;
+       std::set<class ObjectFile::Reader*>                                     fArchiveReadersLogged;
        std::set<class ObjectFile::Atom*>                                       fDeadAtoms;
+       std::set<ObjectFile::Atom*>                                                     fLiveAtoms;
+       std::set<ObjectFile::Atom*>                                                     fLiveRootAtoms;
+       std::vector<class ObjectFile::Reader::Stab>                     fStabs;
+       std::vector<class ObjectFile::Atom*>                            fAtomsWithUnresolvedReferences;
+       std::vector<DTraceProbeInfo>                                            fDtraceProbes;
+       std::vector<DTraceProbeInfo>                                            fDtraceProbeSites;
+       std::vector<DTraceProbeInfo>                                            fDtraceIsEnabledSites;
+       std::map<const ObjectFile::Atom*,CStringSet>            fDtraceAtomToTypes;
+       bool                                                                                            fCreateUUID;
+       bool                                                                                            fCanScatter;
        SectionOrder                                                                            fSectionOrder;
-       unsigned int                                                                            fNextSortOrder;
+       cpu_type_t                                                                                      fArchitecture;
+       const char*                                                                                     fArchitectureName;
+       bool                                                                                            fArchitectureInferred;
        bool                                                                                            fDirectLibrariesComplete;
+       bool                                                                                            fBiggerThanTwoGigOutput;
+       uint64_t                                                                                        fOutputFileSize;
+       uint64_t                                                                                        fTotalZeroFillSize;
+       uint64_t                                                                                        fTotalSize;
+       uint64_t                                                                                        fStartTime;
+       uint64_t                                                                                        fStartCreateReadersTime;
+       uint64_t                                                                                        fStartCreateWriterTime;
+       uint64_t                                                                                        fStartBuildAtomsTime;
+       uint64_t                                                                                        fStartLoadAndResolveTime;
+       uint64_t                                                                                        fStartSortTime;
+       uint64_t                                                                                        fStartDebugTime;
+       uint64_t                                                                                        fStartWriteTime;
+       uint64_t                                                                                        fEndTime;
+       uint64_t                                                                                        fTotalObjectSize;
+       uint64_t                                                                                        fTotalArchiveSize;
+       uint32_t                                                                                        fTotalObjectLoaded;
+       uint32_t                                                                                        fTotalArchivesLoaded;
+       uint32_t                                                                                        fTotalDylibsLoaded;
+       vm_statistics_data_t                                                            fStartVMInfo;
+       ObjectFile::Reader::ObjcConstraint                                      fCurrentObjCConstraint;
+       ObjectFile::Reader::CpuConstraint                                       fCurrentCpuConstraint;
+       bool                                                                                            fObjcReplacmentClasses;
+       bool                                                                                            fAllDirectDylibsLoaded;
 };
 
 
-
 Linker::Linker(int argc, const char* argv[])
- : fOptions(argc, argv), fGlobalSymbolTable(*this), fOutputFile(NULL), fNextSortOrder(1), fDirectLibrariesComplete(false)
+       : fOptions(argc, argv), fGlobalSymbolTable(*this), fNextInputOrdinal(1), fOutputFile(NULL), fBundleLoaderReader(NULL), 
+         fCreateUUID(false), fCanScatter(true),
+         fArchitecture(0), fArchitectureInferred(false), fDirectLibrariesComplete(false), fBiggerThanTwoGigOutput(false),
+         fOutputFileSize(0), fTotalZeroFillSize(0), fTotalSize(0), fTotalObjectSize(0),
+         fTotalArchiveSize(0),  fTotalObjectLoaded(0), fTotalArchivesLoaded(0), fTotalDylibsLoaded(0),
+         fCurrentObjCConstraint(ObjectFile::Reader::kObjcNone), fCurrentCpuConstraint(ObjectFile::Reader::kCpuAny),
+         fObjcReplacmentClasses(false), fAllDirectDylibsLoaded(false)
+{
+       fStartTime = mach_absolute_time();
+       if ( fOptions.printStatistics() )
+               getVMInfo(fStartVMInfo);
+
+       fArchitecture = fOptions.architecture();
+       if ( fArchitecture == 0 ) {
+               // -arch not specified, scan .o files to figure out what it should be
+               fArchitecture = inferArchitecture();
+               fArchitectureInferred = true;
+       }
+       switch (fArchitecture) {
+               case CPU_TYPE_POWERPC:
+                       fArchitectureName = "ppc";
+                       break;
+               case CPU_TYPE_POWERPC64:
+                       fArchitectureName = "ppc64";
+                       break;
+               case CPU_TYPE_I386:
+                       fArchitectureName = "i386";
+                       break;
+               case CPU_TYPE_X86_64:
+                       fArchitectureName = "x86_64";
+                       break;
+               default:
+                       fArchitectureName = "unknown architecture";
+                       break;
+       }
+}
+
+const char*    Linker::architectureName()
+{
+       return fArchitectureName;
+}
+
+bool Linker::showArchitectureInErrors()
+{
+       return fOptions.printArchPrefix();
+}
+
+bool Linker::isInferredArchitecture()
+{
+       return fArchitectureInferred;
+}
+
+cpu_type_t Linker::inferArchitecture()
 {
+       // scan all input files, looking for a thin .o file.
+       // the first one found is presumably the architecture to link
+       uint8_t buffer[sizeof(mach_header_64)];
+       std::vector<Options::FileInfo>& files = fOptions.getInputFiles();
+       for (std::vector<Options::FileInfo>::iterator it = files.begin(); it != files.end(); ++it) {
+               int fd = ::open(it->path, O_RDONLY, 0);
+               if ( fd != -1 ) {
+                       ssize_t amount = read(fd, buffer, sizeof(buffer));
+                       ::close(fd);
+                       if ( amount >= (ssize_t)sizeof(buffer) ) {
+                               if ( mach_o::relocatable::Reader<ppc>::validFile(buffer) ) {
+                                       //fprintf(stderr, "ld: warning -arch not used, infering -arch ppc based on %s\n", it->path);
+                                       return CPU_TYPE_POWERPC;
+                               }
+                               else if ( mach_o::relocatable::Reader<ppc64>::validFile(buffer) ) {
+                                       //fprintf(stderr, "ld: warning -arch not used, infering -arch ppc64 based on %s\n", it->path);
+                                       return CPU_TYPE_POWERPC64;
+                               }
+                               else if ( mach_o::relocatable::Reader<x86>::validFile(buffer) ) {
+                                       //fprintf(stderr, "ld: warning -arch not used, infering -arch i386 based on %s\n", it->path);
+                                       return CPU_TYPE_I386;
+                               }
+                               else if ( mach_o::relocatable::Reader<x86_64>::validFile(buffer) ) {
+                                       //fprintf(stderr, "ld: warning -arch not used, infering -arch x86_64 based on %s\n", it->path);
+                                       return CPU_TYPE_X86_64;
+                               }
+                       }
+               }
+       }
+
+       // no thin .o files found, so default to same architecture this was built as
+       fprintf(stderr, "ld: warning -arch not specified\n");
+#if __ppc__
+       return CPU_TYPE_POWERPC;
+#elif __i386__
+       return CPU_TYPE_I386;
+#elif __ppc64__
+       return CPU_TYPE_POWERPC64;
+#elif __x86_64__
+       return CPU_TYPE_X86_64;
+#else
+       #error unknown default architecture
+#endif
 }
 
-void Linker::addInputFile(ObjectFile::Reader* reader)
+
+void Linker::addInputFile(ObjectFile::Reader* reader, const Options::FileInfo& info)
 {
        fInputFiles.push_back(reader);
+       fDylibOptionsMap[reader] = info.options;
 }
 
 void Linker::setOutputFile(ExecutableFile::Writer* writer)
@@ -355,39 +496,205 @@ void Linker::setOutputFile(ExecutableFile::Writer* writer)
        fOutputFile = writer;
 }
 
+class InSet
+{
+public:
+       InSet(std::set<ObjectFile::Atom*>& deadAtoms) : fDeadAtoms(deadAtoms) {}
+
+       bool operator()(ObjectFile::Atom*& atom) const {
+               return ( fDeadAtoms.count(atom) != 0 );
+       }
+
+private:
+       std::set<ObjectFile::Atom*>& fDeadAtoms;
+};
+
+void Linker::loadAndResolve()
+{
+       fStartLoadAndResolveTime = mach_absolute_time();
+       if ( fOptions.deadStrip() == Options::kDeadStripOff ) {
+               // without dead-code-stripping:
+               // find atoms to resolve all undefines
+               this->loadUndefines();
+               // verify nothing is missing
+               this->checkUndefines();
+               // once all undefines fulfill, then bind all references
+               this->resolveReferences();
+               // remove atoms weak atoms that have been overridden
+               fAllAtoms.erase(std::remove_if(fAllAtoms.begin(), fAllAtoms.end(), InSet(fDeadAtoms)), fAllAtoms.end());
+       }
+       else {
+               // with dead code stripping:
+               // start binding references from roots,
+               this->deadStripResolve();
+               // verify nothing is missing
+               this->checkUndefines();
+       }
+}
+
+void Linker::optimize()
+{
+       std::vector<class ObjectFile::Atom*> newAtoms;
+
+       const int readerCount = fInputFiles.size();
+       for (int i=0; i < readerCount; ++i) {
+               fInputFiles[i]->optimize(fAllAtoms, newAtoms, fNextInputOrdinal);
+       }
+       // note: When writer start generating stubs and non-lazy-pointers for all architecture, do not insert
+       // newAtoms into fGlobalSymbolTable. Instead directly insert them in fAllAtoms and set their order appropriately.
+       this->addAtoms(newAtoms);
+
+       // Some of the optimized atoms may not have identified section properly, if they
+       // were created before optimizer produces corrosponding real atom. Here, input
+       // file readers are not able to patch it themselves because Section::find() is
+       // linker specific.
+       for(std::vector<class ObjectFile::Atom*>::iterator itr = fAllAtoms.begin();
+               itr != fAllAtoms.end(); ++itr) {
+
+               ObjectFile::Atom *atom = *itr;
+               if (atom->getSectionName() && !atom->getSection())
+                       atom->setSection(Section::find(atom->getSectionName(), atom->getSegment().getName(), atom->isZeroFill()));
+       }
+
+       if ( fOptions.deadStrip() != Options::kDeadStripOff ) {
+               fLiveAtoms.clear();
+        deadStripResolve();
+    }
+    else
+        resolveReferences();
+}
+
 void Linker::link()
-{      
+{
        this->buildAtomList();
-       this->loadUndefines();
-       this->resolveReferences();
-       this->deadStrip();
-       this->sortAtoms();
+       this->loadAndResolve();
+       this->optimize();
+       this->checkObjC();
+       this->processDTrace();
        this->tweakLayout();
+       this->sortSections();
+       this->sortAtoms();
+       this->writeDotOutput();
+       this->collectDebugInfo();
        this->writeOutput();
+       this->printStatistics();
+
+       if ( fOptions.pauseAtEnd() )
+               sleep(10);
+}
+
+void Linker::printTime(const char* msg, uint64_t partTime, uint64_t totalTime)
+{
+       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;
+                       //fprintf(stderr, "sUnitsPerSecond=%llu\n", sUnitsPerSecond);
+               }
+       }
+       if ( partTime < sUnitsPerSecond ) {
+               uint32_t milliSecondsTimeTen = (partTime*10000)/sUnitsPerSecond;
+               uint32_t milliSeconds = milliSecondsTimeTen/10;
+               uint32_t percentTimesTen = (partTime*1000)/totalTime;
+               uint32_t percent = percentTimesTen/10;
+               fprintf(stderr, "%s: %u.%u milliseconds (%u.%u%%)\n", msg, milliSeconds, milliSecondsTimeTen-milliSeconds*10, percent, percentTimesTen-percent*10);
+       }
+       else {
+               uint32_t secondsTimeTen = (partTime*10)/sUnitsPerSecond;
+               uint32_t seconds = secondsTimeTen/10;
+               uint32_t percentTimesTen = (partTime*1000)/totalTime;
+               uint32_t percent = percentTimesTen/10;
+               fprintf(stderr, "%s: %u.%u seconds (%u.%u%%)\n", msg, seconds, secondsTimeTen-seconds*10, percent, percentTimesTen-percent*10);
+       }
+}
+
+char* Linker::commatize(uint64_t in, char* out)
+{
+       char* result = out;
+       char rawNum[30];
+       sprintf(rawNum, "%llu", in);
+       const int rawNumLen = strlen(rawNum);
+       for(int i=0; i < rawNumLen-1; ++i) {
+               *out++ = rawNum[i];
+               if ( ((rawNumLen-i) % 3) == 1 )
+                       *out++ = ',';
+       }
+       *out++ = rawNum[rawNumLen-1];
+       *out = '\0';
+       return result;
+}
+
+void Linker::getVMInfo(vm_statistics_data_t& info)
+{
+       mach_msg_type_number_t count = sizeof(vm_statistics_data_t) / sizeof(natural_t);
+       kern_return_t error = host_statistics(mach_host_self(), HOST_VM_INFO,
+                                                       (host_info_t)&info, &count);
+       if (error != KERN_SUCCESS) {
+               bzero(&info, sizeof(vm_statistics_data_t));
+       }
+}
+
+void Linker::printStatistics()
+{
+       fEndTime = mach_absolute_time();
+       if ( fOptions.printStatistics() ) {
+               vm_statistics_data_t endVMInfo;
+               getVMInfo(endVMInfo);
+
+               uint64_t totalTime = fEndTime - fStartTime;
+               printTime("ld total time", totalTime, totalTime);
+               printTime(" option parsing time",       fStartCreateReadersTime -       fStartTime,                                     totalTime);
+               printTime(" object file processing",fStartCreateWriterTime -    fStartCreateReadersTime,        totalTime);
+               printTime(" output file setup",         fStartBuildAtomsTime -          fStartCreateWriterTime,         totalTime);
+               printTime(" build atom list",           fStartLoadAndResolveTime -      fStartBuildAtomsTime,           totalTime);
+               printTime(" resolve references",        fStartSortTime -                        fStartLoadAndResolveTime,       totalTime);
+               printTime(" sort output",                       fStartDebugTime -                       fStartSortTime,                         totalTime);
+               printTime(" process debug info",        fStartWriteTime -                       fStartDebugTime,                        totalTime);
+               printTime(" write output",                      fEndTime -                                      fStartWriteTime,                        totalTime);
+               fprintf(stderr, "pageins=%u, pageouts=%u, faults=%u\n", endVMInfo.pageins-fStartVMInfo.pageins,
+                                                                               endVMInfo.pageouts-fStartVMInfo.pageouts, endVMInfo.faults-fStartVMInfo.faults);
+               char temp[40];
+               fprintf(stderr, "processed %3u object files,  totaling %15s bytes\n", fTotalObjectLoaded, commatize(fTotalObjectSize, temp));
+               fprintf(stderr, "processed %3u archive files, totaling %15s bytes\n", fTotalArchivesLoaded, commatize(fTotalArchiveSize, temp));
+               fprintf(stderr, "processed %3u dylib files\n", fTotalDylibsLoaded);
+               fprintf(stderr, "wrote output file            totaling %15s bytes\n", commatize(fOutputFileSize, temp));
+       }
 }
 
 inline void Linker::addAtom(ObjectFile::Atom& atom)
 {
        // add to list of all atoms
        fAllAtoms.push_back(&atom);
-       
-       // add atom's references's names to symbol table as to-be-resolved-later
-       std::vector<class ObjectFile::Reference*>& references = atom.getReferences();
-       for (std::vector<ObjectFile::Reference*>::iterator it=references.begin(); it != references.end(); it++) {
-               ObjectFile::Reference* reference = *it;
-               if ( reference->isTargetUnbound() ) {
-                       fGlobalSymbolTable.require(reference->getTargetName());
+
+       if ( fOptions.deadStrip() == Options::kDeadStripOff ) {
+               // not dead-stripping code, so add atom's references's names to symbol table as to-be-resolved-later
+               std::vector<class ObjectFile::Reference*>& references = atom.getReferences();
+               for (std::vector<ObjectFile::Reference*>::iterator it=references.begin(); it != references.end(); it++) {
+                       ObjectFile::Reference* reference = *it;
+                       if ( reference->getTargetBinding() == ObjectFile::Reference::kUnboundByName )
+                               fGlobalSymbolTable.require(reference->getTargetName());
+                       if ( reference->getFromTargetBinding() == ObjectFile::Reference::kUnboundByName )
+                               fGlobalSymbolTable.require(reference->getFromTargetName());
+                       if ( reference->getTargetBinding() == ObjectFile::Reference::kDontBind )
+                               addDtraceProbe(atom, reference->getFixUpOffset(), reference->getTargetName());
+               }
+               // update total size info (except for __ZEROPAGE atom)
+               if ( atom.getSegment().isContentReadable() ) {
+                       fTotalSize += atom.getSize();
+                       if ( atom.isZeroFill() )
+                               fTotalZeroFillSize += atom.getSize();
                }
-               if ( reference->hasFromTarget() && reference->isFromTargetUnbound() )
-                       fGlobalSymbolTable.require(reference->getFromTargetName());
        }
-       
+       else {
+               if ( atom.dontDeadStrip() )
+                       fLiveRootAtoms.insert(&atom);
+       }
+
        // if in global namespace, add atom itself to symbol table
        ObjectFile::Atom::Scope scope = atom.getScope();
        const char* name = atom.getName();
        if ( (scope != ObjectFile::Atom::scopeTranslationUnit) && (name != NULL) ) {
-               fGlobalSymbolTable.add(atom);
-               
                // update scope based on export list (possible that globals are downgraded to private_extern)
                if ( (scope == ObjectFile::Atom::scopeGlobal) && fOptions.hasExportRestrictList() ) {
                        bool doExport = fOptions.shouldExport(name);
@@ -395,47 +702,145 @@ inline void Linker::addAtom(ObjectFile::Atom& atom)
                                atom.setScope(ObjectFile::Atom::scopeLinkageUnit);
                        }
                }
+               // add to symbol table
+               fGlobalSymbolTable.add(atom);
        }
-               
+
        // record section orders so output file can have same order
-       atom.setSection(Section::find(atom.getSectionName(), atom.getSegment().getName(), atom.isZeroFill()));
-       
-       // assign order in which this atom was originally seen
-       if ( atom.getSortOrder() == 0 )
-               fNextSortOrder = atom.setSortOrder(fNextSortOrder);
+       if (atom.getSectionName())
+               atom.setSection(Section::find(atom.getSectionName(), atom.getSegment().getName(), atom.isZeroFill()));
+}
+
+void Linker::updateContraints(ObjectFile::Reader* reader)
+{
+       // check objc objects were compiled compatibly
+       ObjectFile::Reader::ObjcConstraint objcAddition = reader->getObjCConstraint();
+       if ( reader->getInstallPath() == NULL ) {
+               // adding a .o file
+               switch ( fCurrentObjCConstraint ) {
+                       case ObjectFile::Reader::kObjcNone:
+                               fCurrentObjCConstraint = objcAddition;
+                               break;
+                       case ObjectFile::Reader::kObjcRetainRelease:
+                       case ObjectFile::Reader::kObjcRetainReleaseOrGC:
+                       case ObjectFile::Reader::kObjcGC:
+                               if ( (fCurrentObjCConstraint != objcAddition) && (objcAddition != ObjectFile::Reader::kObjcNone) ) 
+                                       throwf("%s built with different Garbage Collection settings", reader->getPath());
+                               break;
+               }
+       }
+       if ( reader->objcReplacementClasses() )
+               fObjcReplacmentClasses = true;
+
+       // check cpu sub-types
+       ObjectFile::Reader::CpuConstraint  cpuAddition = reader->getCpuConstraint();
+       switch ( fCurrentCpuConstraint ) {
+               case ObjectFile::Reader::kCpuAny:
+                       fCurrentCpuConstraint = cpuAddition;
+                       break;
+               case ObjectFile::Reader::kCpuG3:
+                       switch ( cpuAddition ) {
+                               case ObjectFile::Reader::kCpuAny:
+                               case ObjectFile::Reader::kCpuG3:
+                                       break;
+                               case ObjectFile::Reader::kCpuG4:
+                               case ObjectFile::Reader::kCpuG5:
+                                       // previous file for G3 this one is more contrained, use it
+                                       fCurrentCpuConstraint = cpuAddition;
+                                       break;
+                       }
+                       break;
+               case ObjectFile::Reader::kCpuG4:
+                       switch ( cpuAddition ) {
+                               case ObjectFile::Reader::kCpuAny:
+                               case ObjectFile::Reader::kCpuG3:
+                               case ObjectFile::Reader::kCpuG4:
+                                       break;
+                               case ObjectFile::Reader::kCpuG5:
+                                       // previous file for G5 this one is more contrained, use it
+                                       fCurrentCpuConstraint = cpuAddition;
+                                       break;
+                       }
+                       break;
+               case ObjectFile::Reader::kCpuG5:
+                       // G5 can run everything
+                       break;
+       }
 }
 
 inline void Linker::addAtoms(std::vector<class ObjectFile::Atom*>& atoms)
 {
+       bool scanAll = fOptions.readerOptions().fFullyLoadArchives || fOptions.readerOptions().fLoadAllObjcObjectsFromArchives;
+       bool first = true; 
        for (std::vector<ObjectFile::Atom*>::iterator it=atoms.begin(); it != atoms.end(); it++) {
+               // usually we only need to get the first atom's reader, but
+               // with -all_load all atoms from all .o files come come back together
+               // so we need to scan all atoms
+               if ( first || scanAll ) {
+                       // update fReadersThatHaveSuppliedAtoms
+                       ObjectFile::Reader* reader = (*it)->getFile();
+                       if ( std::find(fReadersThatHaveSuppliedAtoms.begin(), fReadersThatHaveSuppliedAtoms.end(), reader)
+                                       == fReadersThatHaveSuppliedAtoms.end() ) {
+                               fReadersThatHaveSuppliedAtoms.push_back(reader);
+                               updateContraints(reader);                               
+                       }       
+               }
                this->addAtom(**it);
+               first = false;
+       }
+}
+
+void Linker::logArchive(ObjectFile::Reader* reader)
+{
+       if ( (fArchiveReaders.count(reader) != 0) && (fArchiveReadersLogged.count(reader) == 0) ) {
+               fArchiveReadersLogged.insert(reader);
+               const char* fullPath = reader->getPath();
+               char realName[MAXPATHLEN];
+               if ( realpath(fullPath, realName) != NULL )
+                       fullPath = realName;
+               logTraceInfo("[Logging for XBS] Used static archive: %s\n", fullPath);
        }
 }
 
+
 void Linker::buildAtomList()
 {
+       fStartBuildAtomsTime = mach_absolute_time();
        // add initial undefines from -u option
        std::vector<const char*>& initialUndefines = fOptions.initialUndefines();
        for (std::vector<const char*>::iterator it=initialUndefines.begin(); it != initialUndefines.end(); it++) {
                fGlobalSymbolTable.require(*it);
        }
-       
-       // writer can contribute atoms 
+
+       // writer can contribute atoms
        this->addAtoms(fOutputFile->getAtoms());
-       
+
        // each reader contributes atoms
-       const int readerCount = fInputFiles.size();
-       for (int i=0; i < readerCount; ++i) {
-               this->addAtoms(fInputFiles[i]->getAtoms());
+       for (std::vector<class ObjectFile::Reader*>::iterator it=fInputFiles.begin(); it != fInputFiles.end(); it++) {
+               ObjectFile::Reader* reader = *it;
+               std::vector<class ObjectFile::Atom*>& atoms = reader->getAtoms();
+               this->addAtoms(atoms);
+               if ( fOptions.readerOptions().fTraceArchives && (atoms.size() != 0) ) 
+                       logArchive(reader);
        }
-       
+
        // extra command line section always at end
        std::vector<Options::ExtraSection>& extraSections = fOptions.extraSections();
        for( std::vector<Options::ExtraSection>::iterator it=extraSections.begin(); it != extraSections.end(); ++it) {
-               this->addAtoms(SectCreate::MakeReader(it->segmentName, it->sectionName, it->path, it->data, it->dataLen)->getAtoms());
+               this->addAtoms((new opaque_section::Reader(it->segmentName, it->sectionName, it->path, it->data, it->dataLen, fNextInputOrdinal))->getAtoms());
+               fNextInputOrdinal += it->dataLen;
        }
 }
 
+static const char* pathLeafName(const char* path)
+{
+       const char* shortPath = strrchr(path, '/');
+       if ( shortPath == NULL )
+               return path;
+       else
+               return &shortPath[1];
+}
+
 void Linker::loadUndefines()
 {
        // keep looping until no more undefines were added in last loop
@@ -443,269 +848,224 @@ void Linker::loadUndefines()
        while ( undefineCount != fGlobalSymbolTable.getRequireCount() ) {
                undefineCount = fGlobalSymbolTable.getRequireCount();
                std::vector<const char*> undefineNames;
-               fGlobalSymbolTable.getNeededNames(true, undefineNames);
-               const int undefineCount = undefineNames.size();
-               for (int i=0; i < undefineCount; ++i) {
-                       const char* name = undefineNames[i];
+               fGlobalSymbolTable.getNeededNames(false, undefineNames);
+               for(std::vector<const char*>::iterator it = undefineNames.begin(); it != undefineNames.end(); ++it) {
+                       const char* name = *it;
                        ObjectFile::Atom* possibleAtom = fGlobalSymbolTable.find(name);
-                       if ( (possibleAtom == NULL) || (possibleAtom->isWeakDefinition() && (fOptions.outputKind() != Options::kObjectFile)) )
-                               this->addJustInTimeAtoms(name);
+                       if ( (possibleAtom == NULL)
+                         || ((possibleAtom->getDefinitionKind()==ObjectFile::Atom::kWeakDefinition) 
+                         && (fOptions.outputKind() != Options::kObjectFile) 
+                         && (possibleAtom->getScope() == ObjectFile::Atom::scopeGlobal)) ) {
+                               std::vector<class ObjectFile::Atom*>* atoms = this->addJustInTimeAtoms(name);
+                               if ( atoms != NULL ) 
+                                       delete atoms;
+                       }
                }
        }
-       
-       if ( fOptions.outputKind() != Options::kObjectFile ) {
-               // error out on any remaining undefines
-               bool doPrint = true;
-               bool doError = true;
-               switch ( fOptions.undefinedTreatment() ) {
-                       case Options::kUndefinedError:
-                               break;
-                       case Options::kUndefinedDynamicLookup:
-                               doError = false;
-                               break;
-                       case Options::kUndefinedWarning:
-                               doError = false;
-                               break;
-                       case Options::kUndefinedSuppress:
-                               doError = false;
-                               doPrint = false;
-                               break;
+}
+
+// temp hack for rdar://problem/4718189 map ObjC class names to new runtime names
+class ExportedObjcClass
+{
+public:
+       ExportedObjcClass(Options& opt) : fOptions(opt)  {}
+
+       bool operator()(const char* name) const {
+               if ( fOptions.shouldExport(name) ) {
+                       if ( strncmp(name, ".objc_class_name_", 17) == 0 )
+                               return true;
+                       if ( strncmp(name, "_OBJC_CLASS_$_", 14) == 0 )
+                               return true;
+                       if ( strncmp(name, "_OBJC_METACLASS_$_", 18) == 0 )
+                               return true;
                }
-               std::vector<const char*> unresolvableUndefines;
-               fGlobalSymbolTable.getNeededNames(false, unresolvableUndefines);
-               const int unresolvableCount = unresolvableUndefines.size();
-               int unresolvableExportsCount  = 0;
-               if ( unresolvableCount != 0 ) {
-                       if ( doPrint ) {
-                               fprintf(stderr, "can't resolve symbols:\n");
-                               for (int i=0; i < unresolvableCount; ++i) {
-                                       const char* name = unresolvableUndefines[i];
-                                       const unsigned int nameLen = strlen(name);
-                                       fprintf(stderr, "  %s, referenced from:\n", name);
-                                       char stubName[nameLen+6];
-                                       strcpy(stubName, name);
-                                       strcat(stubName, "$stub");
-                                       char nonLazyName[nameLen+16];
-                                       strcpy(nonLazyName, name);
-                                       strcat(nonLazyName, "$non_lazy_ptr");
-                                       ObjectFile::Atom* lastStubAtomWithUnresolved = NULL;
-                                       ObjectFile::Atom* lastNonLazyAtomWithUnresolved = NULL;
-                                       // scan all atoms for references
-                                       bool foundAtomReference = false;
-                                       for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
-                                               ObjectFile::Atom* atom = *it;
-                                               std::vector<class ObjectFile::Reference*>& references = atom->getReferences();
-                                               for (std::vector<ObjectFile::Reference*>::iterator rit=references.begin(); rit != references.end(); rit++) {
-                                                       ObjectFile::Reference* reference = *rit;
-                                                       if ( reference->isTargetUnbound() ) {
-                                                               if ( (atom != lastStubAtomWithUnresolved) && (strcmp(reference->getTargetName(), stubName) == 0) ) {
-                                                                       const char* path = atom->getFile()->getPath();
-                                                                       const char* shortPath = strrchr(path, '/');
-                                                                       if ( shortPath == NULL )
-                                                                               shortPath = path;
-                                                                       else
-                                                                               shortPath = &shortPath[1];
-                                                                       fprintf(stderr, "      %s in %s\n", atom->getDisplayName(), shortPath);
-                                                                       lastStubAtomWithUnresolved = atom;
-                                                                       foundAtomReference = true;
-                                                               }
-                                                               else if ( (atom != lastNonLazyAtomWithUnresolved) && (strcmp(reference->getTargetName(), nonLazyName) == 0) ) {
-                                                                       const char* path = atom->getFile()->getPath();
-                                                                       const char* shortPath = strrchr(path, '/');
-                                                                       if ( shortPath == NULL )
-                                                                               shortPath = path;
-                                                                       else
-                                                                               shortPath = &shortPath[1];
-                                                                       fprintf(stderr, "      %s in %s\n", atom->getDisplayName(), shortPath);
-                                                                       lastNonLazyAtomWithUnresolved = atom;
-                                                                       foundAtomReference = true;
-                                                               }
+               //fprintf(stderr, "%s is not exported\n", name);
+               return false;
+       }
+private:
+       Options& fOptions;
+};
+
+
+void Linker::checkUndefines()
+{
+       // error out on any remaining undefines
+       bool doPrint = true;
+       bool doError = true;
+       switch ( fOptions.undefinedTreatment() ) {
+               case Options::kUndefinedError:
+                       break;
+               case Options::kUndefinedDynamicLookup:
+                       doError = false;
+                       break;
+               case Options::kUndefinedWarning:
+                       doError = false;
+                       break;
+               case Options::kUndefinedSuppress:
+                       doError = false;
+                       doPrint = false;
+                       break;
+       }
+       std::vector<const char*> unresolvableUndefines;
+       fGlobalSymbolTable.getNeededNames(false, unresolvableUndefines);
+
+       // temp hack for rdar://problem/4718189 map ObjC class names to new runtime names
+       // ignore unresolved references to Objc class names that are listed in -exported_symbols_list
+       if ( fOptions.hasExportRestrictList() )
+               unresolvableUndefines.erase(std::remove_if(unresolvableUndefines.begin(), unresolvableUndefines.end(), ExportedObjcClass(fOptions)), unresolvableUndefines.end());
+
+       const int unresolvableCount = unresolvableUndefines.size();
+       int unresolvableExportsCount  = 0;
+       if ( unresolvableCount != 0 ) {
+               if ( doPrint ) {
+                       if ( fOptions.printArchPrefix() )
+                               fprintf(stderr, "Undefined symbols for architecture %s:\n", fArchitectureName);
+                       else
+                               fprintf(stderr, "Undefined symbols:\n");
+                       for (int i=0; i < unresolvableCount; ++i) {
+                               const char* name = unresolvableUndefines[i];
+                               fprintf(stderr, "  \"%s\", referenced from:\n", name);
+                               // scan all atoms for references
+                               bool foundAtomReference = false;
+                               for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                                       ObjectFile::Atom* atom = *it;
+                                       std::vector<class ObjectFile::Reference*>& references = atom->getReferences();
+                                       for (std::vector<ObjectFile::Reference*>::iterator rit=references.begin(); rit != references.end(); rit++) {
+                                               ObjectFile::Reference* reference = *rit;
+                                               if ( reference->getTargetBinding() == ObjectFile::Reference::kUnboundByName ) {
+                                                       if ( strcmp(reference->getTargetName(), name) == 0 ) {
+                                                               fprintf(stderr, "      %s in %s\n", atom->getDisplayName(), pathLeafName(atom->getFile()->getPath()));
+                                                               foundAtomReference = true;
                                                        }
-                                                       if ( reference->hasFromTarget() && reference->isFromTargetUnbound() ) {
-                                                               if ( (atom != lastStubAtomWithUnresolved) && (strcmp(reference->getFromTargetName(), stubName) == 0) ) {
-                                                                       const char* path = atom->getFile()->getPath();
-                                                                       const char* shortPath = strrchr(path, '/');
-                                                                       if ( shortPath == NULL )
-                                                                               shortPath = path;
-                                                                       else
-                                                                               shortPath = &shortPath[1];
-                                                                       fprintf(stderr, "      %s in %s\n", atom->getDisplayName(), shortPath);
-                                                                       lastStubAtomWithUnresolved = atom;
-                                                                       foundAtomReference = true;
-                                                               }
-                                                               else if ( (atom != lastNonLazyAtomWithUnresolved) && (strcmp(reference->getFromTargetName(), nonLazyName) == 0) ) {
-                                                                       const char* path = atom->getFile()->getPath();
-                                                                       const char* shortPath = strrchr(path, '/');
-                                                                       if ( shortPath == NULL )
-                                                                               shortPath = path;
-                                                                       else
-                                                                               shortPath = &shortPath[1];
-                                                                       fprintf(stderr, "      %s in %s\n", atom->getDisplayName(), shortPath);
-                                                                       lastNonLazyAtomWithUnresolved = atom;
-                                                                       foundAtomReference = true;
-                                                               }
+                                               }
+                                               if ( reference->getFromTargetBinding() == ObjectFile::Reference::kUnboundByName ) {
+                                                       if ( strcmp(reference->getFromTargetName(), name) == 0 ) {
+                                                               fprintf(stderr, "      %s in %s\n", atom->getDisplayName(), pathLeafName(atom->getFile()->getPath()));
+                                                               foundAtomReference = true;
                                                        }
                                                }
                                        }
-                                       // scan command line options
-                                       if  ( !foundAtomReference && fOptions.hasExportRestrictList() && fOptions.shouldExport(name) ) {
-                                               fprintf(stderr, "     -exported_symbols_list command line option\n");
-                                               ++unresolvableExportsCount;
-                                       }
+                               }
+                               // scan command line options
+                               if  ( !foundAtomReference && fOptions.hasExportRestrictList() && fOptions.shouldExport(name) ) {
+                                       fprintf(stderr, "     -exported_symbols_list command line option\n");
+                                       ++unresolvableExportsCount;
                                }
                        }
-                       if ( doError && (unresolvableCount > unresolvableExportsCount) ) // last check should be removed.  It exists so broken projects still build
-                               throw "symbol(s) not found";
-               }
-               
-               // now verify that -init routine exists
-               if ( fOptions.initFunctionName() != NULL ) {
-                       if ( fGlobalSymbolTable.find(fOptions.initFunctionName()) == NULL )
-                               throwf("symbol %s not found for -init", fOptions.initFunctionName());
                }
+               if ( doError ) 
+                       throw "symbol(s) not found";
        }
 }
 
 
 
-void Linker::addJustInTimeAtoms(const char* name)
+std::vector<class ObjectFile::Atom*>* Linker::addJustInTimeAtoms(const char* name)
 {
-       // when creating final linked image, write gets first chance
+       // when creating final linked image, writer gets first chance
        if ( fOptions.outputKind() != Options::kObjectFile ) {
-               ObjectFile::Atom* atom = fOutputFile->getUndefinedProxyAtom(name);
-               if ( atom != NULL ) {
-                       this->addAtom(*atom);\
-                       return;
-               }
-       }
-       
-       // give direct readers a chance
-       const int readerCount = fInputFiles.size();
-       for (int i=0; i < readerCount; ++i) {
-               // if this reader is a static archive that has the symbol we need, pull in all atoms in that module
-               // if this reader is a dylib that exports the symbol we need, have it synthesize an atom for us.
-               std::vector<class ObjectFile::Atom*>* atoms = fInputFiles[i]->getJustInTimeAtomsFor(name);
+               std::vector<class ObjectFile::Atom*>* atoms = fOutputFile->getJustInTimeAtomsFor(name);
                if ( atoms != NULL ) {
                        this->addAtoms(*atoms);
-                       delete atoms;
-                       return;  // found a definition, no need to search anymore
-                       //fprintf(stderr, "addJustInTimeAtoms(%s) => found in file #%d\n", name, i);
+                       //fprintf(stderr, "addJustInTimeAtoms(%s) => found in file %s\n", name, fOutputFile->getPath() );
+                       return atoms;  // found a definition, no need to search anymore
                }
        }
-       
-       // give indirect readers a chance
-       for (std::list<IndirectLibrary>::iterator it=fIndirectDynamicLibraries.begin(); it != fIndirectDynamicLibraries.end(); it++) {
-               ObjectFile::Reader* reader = it->reader;
+
+       // give readers a chance
+       for (std::vector<class ObjectFile::Reader*>::iterator it=fInputFiles.begin(); it != fInputFiles.end(); it++) {
+               ObjectFile::Reader* reader = *it;
                if ( reader != NULL ) {
+                       // if this reader is a static archive that has the symbol we need, pull in all atoms in that module
+                       // if this reader is a dylib that exports the symbol we need, have it synthesize an atom for us.
+                       //fprintf(stderr, "addJustInTimeAtoms(%s), looking in reader %s\n", name, reader->getPath() );
                        std::vector<class ObjectFile::Atom*>* atoms = reader->getJustInTimeAtomsFor(name);
                        if ( atoms != NULL ) {
                                this->addAtoms(*atoms);
-                               delete atoms;
-                               break;
-                               //fprintf(stderr, "addJustInTimeAtoms(%s) => found in file #%d\n", name, i);
+                               //fprintf(stderr, "addJustInTimeAtoms(%s) => found in file %s\n", name, reader->getPath() );
+                               if ( fOptions.readerOptions().fTraceArchives ) {
+                                       logArchive(reader);
+                               }
+                               // if this is a weak definition in a dylib
+                               if ( (atoms->size() == 1) && (reader->getInstallPath() != NULL) && (atoms->at(0)->getDefinitionKind() == ObjectFile::Atom::kExternalWeakDefinition) ) {
+                                       // keep looking for a non-weak definition
+                               }
+                               else {
+                                       // found a definition, no need to search anymore
+                                       return atoms;  
+                               }
                        }
                }
        }
-       
+
+       // for two level namesapce, give all implicitly link dylibs a chance
+       if ( fOptions.nameSpace() == Options::kTwoLevelNameSpace ) {
+               for (InstallNameToReader::iterator it=fDylibMap.begin(); it != fDylibMap.end(); it++) {
+                       if ( it->second->implicitlyLinked() ) {
+                               //fprintf(stderr, "addJustInTimeAtoms(%s), looking in implicitly linked %s\n", name, it->second->getPath() );
+                               std::vector<class ObjectFile::Atom*>* atoms = it->second->getJustInTimeAtomsFor(name);
+                               if ( atoms != NULL ) {
+                                       this->addAtoms(*atoms);
+                                       //fprintf(stderr, "addJustInTimeAtoms(%s) => found in file %s\n", name, reader->getPath() );
+                                       // if this is a weak definition in a dylib
+                                       if ( (atoms->size() == 1) && (atoms->at(0)->getDefinitionKind() == ObjectFile::Atom::kExternalWeakDefinition) ) {
+                                               // keep looking for a non-weak definition
+                                       }
+                                       else {
+                                               // found a definition, no need to search anymore
+                                               return atoms;  
+                                       }
+                               }
+                       }
+               }
+       }
+
+       // for flat namespace, give indirect dylibs
+       if ( fOptions.nameSpace() != Options::kTwoLevelNameSpace ) {
+               for (InstallNameToReader::iterator it=fDylibMap.begin(); it != fDylibMap.end(); it++) {
+                       if ( ! it->second->explicitlyLinked() ) {
+                               std::vector<class ObjectFile::Atom*>* atoms = it->second->getJustInTimeAtomsFor(name);
+                               if ( atoms != NULL ) {
+                                       this->addAtoms(*atoms);
+                                       //fprintf(stderr, "addJustInTimeAtoms(%s) => found in file %s\n", name, reader->getPath() );
+                                       return atoms;  // found a definition, no need to search anymore
+                               }
+                       }
+               }
+       }
+
        // when creating .o file, writer goes last (this is so any static archives will be searched above)
-       if ( fOptions.outputKind() == Options::kObjectFile ) {
+       if (    (fOptions.outputKind() == Options::kObjectFile) 
+               ||  (fOptions.undefinedTreatment() != Options::kUndefinedError)
+               ||      fOptions.someAllowedUndefines() ) {
                ObjectFile::Atom* atom = fOutputFile->getUndefinedProxyAtom(name);
                if ( atom != NULL ) {
                        this->addAtom(*atom);
-                       return;
+                       return NULL;
                }
        }
-
+       //fprintf(stderr, "addJustInTimeAtoms(%s) => not found\n", name);
+       return NULL;
 }
 
 void Linker::resolve(ObjectFile::Reference* reference)
 {
-       ObjectFile::Atom* target = NULL;
-       const char* targetName = reference->getTargetName();
-       const int targetNameLen = strlen(targetName);
-       if ( (targetNameLen > 5) && (strcmp(&targetName[targetNameLen-5], "$stub") == 0) ) {
-               // when looking up "_foo$stub", first look for "_foo"
-               char nonStubTarget[targetNameLen+1];
-               strcpy(nonStubTarget, targetName);
-               nonStubTarget[targetNameLen-5] = '\0';
-               // unless interposing and the symbol is exported 
-               if ( !fOptions.interposable() || !fOptions.shouldExport(nonStubTarget) ) {
-                       target = fGlobalSymbolTable.find(nonStubTarget);        
-                       // also need indirection to all exported weak symbols for C++ support
-                       if ( (target != NULL) && !target->isImportProxy() && (!target->isWeakDefinition() || (target->getScope() != ObjectFile::Atom::scopeGlobal)) ) {
-                               reference->setTarget(*target, reference->getTargetOffset());
-                               // mark stub as no longer being needed
-                               ObjectFile::Atom* stub = fGlobalSymbolTable.find(targetName);
-                               if ( stub != NULL ) {
-                                       char lazySymbol[targetNameLen+8];
-                                       strcpy(lazySymbol, nonStubTarget);
-                                       strcat(lazySymbol, "$lazy_ptr");
-                                       ObjectFile::Atom* lazyPtr = fGlobalSymbolTable.find(lazySymbol);
-                                       fDeadAtoms.insert(stub);
-                                       if ( lazyPtr != NULL )
-                                               fDeadAtoms.insert(lazyPtr);
-                               }
-                               return;
-                       }
-               }
-       }
-       
        // look in global symbol table
-       target = fGlobalSymbolTable.find(targetName);
+       const char* targetName = reference->getTargetName();
+       ObjectFile::Atom* target = fGlobalSymbolTable.find(targetName);
        if ( target == NULL ) {
-               fprintf(stderr, "can't resolve: %s\n", targetName);
+               fprintf(stderr, "Undefined symbol: %s\n", targetName);
        }
        reference->setTarget(*target, reference->getTargetOffset());
-       
-       // handle weak-imports
-       if ( target->isImportProxy() ) {
-               bool mismatch = false;
-               if ( reference->isWeakReference() ) {
-                       switch(target->getImportWeakness()) {
-                               case ObjectFile::Atom::kWeakUnset:
-                                       target->setImportWeakness(true);        
-                                       break;
-                               case ObjectFile::Atom::kWeakImport:
-                                       break;
-                               case ObjectFile::Atom::kNonWeakImport:
-                                       mismatch = true;
-                                       break;
-                       }
-               }
-               else {
-                       switch(target->getImportWeakness()) {
-                               case ObjectFile::Atom::kWeakUnset:
-                                       target->setImportWeakness(false);
-                                       break;  
-                               case ObjectFile::Atom::kWeakImport:
-                                       mismatch = true;
-                                       break;
-                               case ObjectFile::Atom::kNonWeakImport:
-                                       break;
-                       }
-               }
-               if ( mismatch ) {
-                       switch ( fOptions.weakReferenceMismatchTreatment() ) {
-                               case Options::kWeakReferenceMismatchError:
-                                       throwf("mismatching weak references for symbol: %s", target->getName());
-                               case Options::kWeakReferenceMismatchWeak:
-                                       target->setImportWeakness(true);
-                                       break;
-                               case Options::kWeakReferenceMismatchNonWeak:
-                                       target->setImportWeakness(false);
-                                       break;
-                       }
-               }
-       }
 }
 
 void Linker::resolveFrom(ObjectFile::Reference* reference)
-{      
+{
        // handle references that have two (from and to) targets
        const char* fromTargetName = reference->getFromTargetName();
        ObjectFile::Atom* fromTarget = fGlobalSymbolTable.find(fromTargetName);
        if ( fromTarget == NULL ) {
-               fprintf(stderr, "can't resolve: %s\n", fromTargetName);
+               fprintf(stderr, "Undefined symbol: %s\n", fromTargetName);
        }
        reference->setFromTarget(*fromTarget);
 }
@@ -719,59 +1079,932 @@ void Linker::resolveReferences()
                std::vector<class ObjectFile::Reference*>& references = atom->getReferences();
                for (std::vector<ObjectFile::Reference*>::iterator it=references.begin(); it != references.end(); it++) {
                        ObjectFile::Reference* reference = *it;
-                       if ( reference->isTargetUnbound() ) 
+                       if ( reference->getTargetBinding() == ObjectFile::Reference::kUnboundByName )
                                this->resolve(reference);
-                       if ( reference->hasFromTarget() && reference->isFromTargetUnbound() ) 
+                       if ( reference->getFromTargetBinding() == ObjectFile::Reference::kUnboundByName )
                                this->resolveFrom(reference);
                }
        }
 }
 
-class InSet
+
+// used to remove stabs associated with atoms that won't be in output file
+class NotInSet
 {
 public:
-       InSet(std::set<ObjectFile::Atom*>& deadAtoms) : fDeadAtoms(deadAtoms) {}
-       
-       bool operator()(ObjectFile::Atom*& atom) const { 
-               return ( fDeadAtoms.count(atom) != 0 );
+       NotInSet(std::set<ObjectFile::Atom*>& theSet) : fSet(theSet) {}
+
+       bool operator()(const ObjectFile::Reader::Stab& stab) const {
+               if ( stab.atom == NULL )
+                       return false;   // leave stabs that are not associated with any atome
+               else
+                       return ( fSet.count(stab.atom) == 0 );
        }
-       
+
 private:
-       std::set<ObjectFile::Atom*>& fDeadAtoms;
+       std::set<ObjectFile::Atom*>& fSet;
 };
 
 
-void Linker::deadStrip()
+class NotLive
 {
-       //printf("Stripping atoms:\n");
-       //for (std::set<ObjectFile::Atom*>::iterator it=fDeadAtoms.begin(); it != fDeadAtoms.end(); it++) {
-       //      printf("\t%s\n", (*it)->getDisplayName());
-       //}
+public:
+       NotLive(std::set<ObjectFile::Atom*>& set) : fLiveAtoms(set)  {}
+
+       bool operator()(ObjectFile::Atom*& atom) const {
+               //if ( fLiveAtoms.count(atom) == 0 )
+               //      fprintf(stderr, "dead strip %s\n", atom->getDisplayName());
+               return ( fLiveAtoms.count(atom) == 0 );
+       }
+private:
+       std::set<ObjectFile::Atom*>& fLiveAtoms;
+};
+
 
-       // for now, just remove atoms weak atoms that have been overridden
-       fAllAtoms.erase(std::remove_if(fAllAtoms.begin(), fAllAtoms.end(), InSet(fDeadAtoms)), fAllAtoms.end());
+void Linker::addJustInTimeAtomsAndMarkLive(const char* name)
+{
+       std::vector<class ObjectFile::Atom*>* atoms = this->addJustInTimeAtoms(name);
+       if ( atoms != NULL ) {
+               if ( fOptions.allGlobalsAreDeadStripRoots() ) {
+                       for (std::vector<ObjectFile::Atom*>::iterator it=atoms->begin(); it != atoms->end(); it++) {
+                               ObjectFile::Atom* atom = *it;
+                               if ( atom->getScope() ==  ObjectFile::Atom::scopeGlobal ) {
+                                       WhyLiveBackChain rootChain;
+                                       rootChain.previous = NULL;
+                                       rootChain.name = atom->getDisplayName();
+                                       this->markLive(*atom, &rootChain);
+                               }
+                       }
+               }
+               delete atoms;
+       }
+}
+
+void Linker::markLive(ObjectFile::Atom& atom, struct Linker::WhyLiveBackChain* previous)
+{
+       if ( fLiveAtoms.count(&atom) == 0 ) {
+               // if -whylive cares about this symbol, then dump chain
+               if ( (previous->name != NULL) && fOptions.printWhyLive(previous->name) ) {
+                       int depth = 0;
+                       for(WhyLiveBackChain* p = previous; p != NULL; p = p->previous, ++depth) {
+                               for(int i=depth; i > 0; --i)
+                                       fprintf(stderr, "  ");
+                               fprintf(stderr, "%s\n", p->name);
+                       }
+               }
+               // set up next chain
+               WhyLiveBackChain thisChain;
+               thisChain.previous = previous;
+               // this atom is live
+               fLiveAtoms.insert(&atom);
+               // update total size info (except for __ZEROPAGE atom)
+               if ( atom.getSegment().isContentReadable() ) {
+                       fTotalSize += atom.getSize();
+                       if ( atom.isZeroFill() )
+                               fTotalZeroFillSize += atom.getSize();
+               }
+               // and all atoms it references
+               std::vector<class ObjectFile::Reference*>& references = atom.getReferences();
+               for (std::vector<ObjectFile::Reference*>::iterator it=references.begin(); it != references.end(); it++) {
+                       ObjectFile::Reference* reference = *it;
+                       if ( reference->getTargetBinding() == ObjectFile::Reference::kUnboundByName ) {
+                               // look in global symbol table
+                               const char* targetName = reference->getTargetName();
+                               ObjectFile::Atom* target = fGlobalSymbolTable.find(targetName);
+                               if ( target == NULL ) {
+                                       // load archives or dylibs
+                                       this->addJustInTimeAtomsAndMarkLive(targetName);
+                               }
+                               // look again
+                               target = fGlobalSymbolTable.find(targetName);
+                               if ( target != NULL ) {
+                                       reference->setTarget(*target, reference->getTargetOffset());
+                               }
+                               else {
+                                       // mark as undefined, for later error processing
+                                       fAtomsWithUnresolvedReferences.push_back(&atom);
+                                       fGlobalSymbolTable.require(targetName);
+                               }
+                       }
+                       switch ( reference->getTargetBinding() ) {
+                               case ObjectFile::Reference::kBoundDirectly:
+                               case ObjectFile::Reference::kBoundByName:
+                                       thisChain.name = reference->getTargetName();
+                                       markLive(reference->getTarget(), &thisChain);
+                                       break;
+                               case ObjectFile::Reference::kDontBind:
+                                       addDtraceProbe(atom, reference->getFixUpOffset(), reference->getTargetName());
+                                       break;
+                               case ObjectFile::Reference::kUnboundByName:
+                                       // do nothing
+                                       break;
+                       }
+                       // do the same as above, for "from target"
+                       if ( reference->getFromTargetBinding() == ObjectFile::Reference::kUnboundByName ) {
+                               // look in global symbol table
+                               const char* targetName = reference->getFromTargetName();
+                               ObjectFile::Atom* target = fGlobalSymbolTable.find(targetName);
+                               if ( target == NULL ) {
+                                       // load archives or dylibs
+                                       this->addJustInTimeAtomsAndMarkLive(targetName);
+                               }
+                               // look again
+                               target = fGlobalSymbolTable.find(targetName);
+                               if ( target != NULL ) {
+                                       reference->setFromTarget(*target);
+                               }
+                               else {
+                                       // mark as undefined, for later error processing
+                                       fGlobalSymbolTable.require(targetName);
+                               }
+                       }
+                       switch ( reference->getFromTargetBinding() ) {
+                               case ObjectFile::Reference::kBoundDirectly:
+                               case ObjectFile::Reference::kBoundByName:
+                                       thisChain.name = reference->getFromTargetName();
+                                       markLive(reference->getFromTarget(), &thisChain);
+                                       break;
+                               case ObjectFile::Reference::kUnboundByName:
+                               case ObjectFile::Reference::kDontBind:
+                                       // do nothing
+                                       break;
+                       }
+               }
+       }
 }
 
 
+void Linker::addLiveRoot(const char* name)
+{
+       ObjectFile::Atom* target = fGlobalSymbolTable.find(name);
+       if ( target == NULL ) {
+               this->addJustInTimeAtomsAndMarkLive(name);
+               target = fGlobalSymbolTable.find(name);
+       }
+       if ( target != NULL )
+               fLiveRootAtoms.insert(target);
+}
 
-void Linker::sortAtoms()
+
+void Linker::deadStripResolve()
+{
+       // add main() to live roots
+       ObjectFile::Atom* entryPoint = this->entryPoint();
+       if ( entryPoint != NULL )
+               fLiveRootAtoms.insert(entryPoint);
+
+       // add dyld_stub_binding_helper() to live roots
+       ObjectFile::Atom* dyldHelper = this->dyldHelper();
+       if ( dyldHelper != NULL )
+               fLiveRootAtoms.insert(dyldHelper);
+
+       // add -exported_symbols_list, -init, and -u entries to live roots
+       std::vector<const char*>& initialUndefines = fOptions.initialUndefines();
+       for (std::vector<const char*>::iterator it=initialUndefines.begin(); it != initialUndefines.end(); it++)
+               addLiveRoot(*it);
+
+       // in some cases, every global scope atom in initial .o files is a root
+       if ( fOptions.allGlobalsAreDeadStripRoots() ) {
+               for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                       ObjectFile::Atom* atom = *it;
+                       if ( (atom->getScope() == ObjectFile::Atom::scopeGlobal) && (fDeadAtoms.count(atom) == 0) )
+                               fLiveRootAtoms.insert(atom);
+               }
+       }
+
+       // mark all roots as live, and all atoms they reference
+       for (std::set<ObjectFile::Atom*>::iterator it=fLiveRootAtoms.begin(); it != fLiveRootAtoms.end(); it++) {
+               WhyLiveBackChain rootChain;
+               rootChain.previous = NULL;
+               rootChain.name = (*it)->getDisplayName();
+               markLive(**it, &rootChain);
+       }
+
+       // it is possible that there are unresolved references that can be resolved now
+       // this can happen if the first reference to a common symbol in an archive.
+       // common symbols are not in the archive TOC, but the .o could have been pulled in later.
+       // <rdar://problem/4654131> ld64 while linking cc1 [ when dead_strip is ON]
+       for (std::vector<ObjectFile::Atom*>::iterator it=fAtomsWithUnresolvedReferences.begin(); it != fAtomsWithUnresolvedReferences.end(); it++) {
+               std::vector<class ObjectFile::Reference*>& references = (*it)->getReferences();
+               for (std::vector<ObjectFile::Reference*>::iterator rit=references.begin(); rit != references.end(); rit++) {
+                       ObjectFile::Reference* reference = *rit;
+                       if ( reference->getTargetBinding() == ObjectFile::Reference::kUnboundByName ) {
+                               ObjectFile::Atom* target = fGlobalSymbolTable.find(reference->getTargetName());
+                               if ( target != NULL ) {
+                                       reference->setTarget(*target, reference->getTargetOffset());
+                                       fLiveAtoms.insert(target);
+                                       // by just adding this atom to fLiveAtoms set, we are assuming it has no
+                                       // references, which is true for commons.
+                                       if ( target->getDefinitionKind() != ObjectFile::Atom::kTentativeDefinition )
+                                               fprintf(stderr, "warning: ld64 internal error %s is not a tentative definition\n", target->getDisplayName());
+                               }
+                       }
+                       if ( reference->getFromTargetBinding() == ObjectFile::Reference::kUnboundByName ) {
+                               ObjectFile::Atom* target = fGlobalSymbolTable.find(reference->getFromTargetName());
+                               if ( target != NULL ) {
+                                       reference->setFromTarget(*target);
+                                       fLiveAtoms.insert(target);
+                                       // by just adding this atom to fLiveAtoms set, we are assuming it has no
+                                       // references, which is true for commons.
+                                       if ( target->getDefinitionKind() != ObjectFile::Atom::kTentativeDefinition )
+                                               fprintf(stderr, "warning: ld64 internal error %s is not a tentative definition\n", target->getDisplayName());
+                               }
+                       }
+               }
+       }
+
+       // now remove all non-live atoms from fAllAtoms
+       fAllAtoms.erase(std::remove_if(fAllAtoms.begin(), fAllAtoms.end(), NotLive(fLiveAtoms)), fAllAtoms.end());
+}
+
+void Linker::checkObjC()
+{
+       // check dylibs
+       switch ( fCurrentObjCConstraint ) {
+               case ObjectFile::Reader::kObjcNone:
+                       // can link against any dylib
+                       break;
+               case ObjectFile::Reader::kObjcRetainRelease:
+                       // cannot link against GC-only dylibs
+                       for (InstallNameToReader::iterator it=fDylibMap.begin(); it != fDylibMap.end(); it++) {
+                               if ( it->second->explicitlyLinked() ) {
+                                       if ( it->second->getObjCConstraint() == ObjectFile::Reader::kObjcGC )
+                                               throwf("this linkage unit uses Retain/Release.  It cannot link against the GC-only dylib: %s", it->second->getPath());
+                               }
+                       }
+                       break;
+               case ObjectFile::Reader::kObjcRetainReleaseOrGC:
+                       // can link against GC or RR dylibs
+                       break;
+               case ObjectFile::Reader::kObjcGC:
+                       // cannot link against RR-only dylibs
+                       for (InstallNameToReader::iterator it=fDylibMap.begin(); it != fDylibMap.end(); it++) {
+                               if ( it->second->explicitlyLinked() ) {
+                                       if ( it->second->getObjCConstraint() == ObjectFile::Reader::kObjcRetainRelease )
+                                               throwf("this linkage unit requires GC.  It cannot link against Retain/Release dylib: %s", it->second->getPath());
+                               }
+                       }
+                       break;
+       }
+       
+       // synthesize __OBJC __image_info atom if needed
+       if ( fCurrentObjCConstraint != ObjectFile::Reader::kObjcNone ) {
+               this->addAtom(fOutputFile->makeObjcInfoAtom(fCurrentObjCConstraint, fObjcReplacmentClasses));
+       }
+}
+
+void Linker::addDtraceProbe(ObjectFile::Atom& atom, uint32_t offsetInAtom, const char* probeName)
+{
+       if ( probeName != NULL ) {
+               if ( strncmp(probeName, "___dtrace_probe$", 16) == 0 ) 
+                       fDtraceProbeSites.push_back(DTraceProbeInfo(&atom, offsetInAtom, probeName));
+               else if ( strncmp(probeName, "___dtrace_isenabled$", 20) == 0 ) 
+                       fDtraceIsEnabledSites.push_back(DTraceProbeInfo(&atom, offsetInAtom, probeName));
+               else if ( strncmp(probeName, "___dtrace_", 10) == 0 )
+                       fDtraceAtomToTypes[&atom].insert(probeName);
+               else if ( fOptions.dTrace() && (strncmp(probeName, "__dtrace_probe$", 15) == 0) ) 
+                       fDtraceProbes.push_back(DTraceProbeInfo(&atom, offsetInAtom, probeName));
+       }
+}
+
+static uint8_t pointerKind(cpu_type_t arch)
+{
+       switch ( arch ) {
+               case CPU_TYPE_POWERPC:
+                       return ppc::kPointer;
+               case CPU_TYPE_POWERPC64:
+                       return ppc64::kPointer;
+               case CPU_TYPE_I386:
+                       return x86::kPointer;
+               case CPU_TYPE_X86_64:
+                       return x86_64::kPointer;
+       }
+       throw "uknown architecture";
+}
+
+static uint8_t pcRelKind(cpu_type_t arch)
+{
+       switch ( arch ) {
+               case CPU_TYPE_POWERPC:
+                       return ppc::kPointerDiff32;
+               case CPU_TYPE_POWERPC64:
+                       return ppc64::kPointerDiff32;
+               case CPU_TYPE_I386:
+                       return x86::kPointerDiff;
+               case CPU_TYPE_X86_64:
+                       return x86_64::kPointerDiff32;
+       }
+       throw "uknown architecture";
+}
+
+typedef uint8_t* (*oldcreatedof_func_t) (const char*, cpu_type_t, unsigned int, const char*[], const char*[], uint64_t offsetsInDOF[], size_t* size);
+typedef uint8_t* (*createdof_func_t)(cpu_type_t, unsigned int, const char*[], unsigned int, const char*[], const char*[], uint64_t offsetsInDOF[], size_t* size);
+
+
+void Linker::processDTrace()
+{
+       // handle dtrace 2.0 static probes
+       if ( (fOptions.outputKind() != Options::kObjectFile) && ((fDtraceProbeSites.size() != 0) || (fDtraceIsEnabledSites.size() != 0)) ) {
+               // partition probes by provider name
+               // The symbol names looks like:
+               //      "___dtrace_isenabled$" provider-name "$" probe-name [ "$"... ]
+               //      "___dtrace_probe$" provider-name "$" probe-name [ "$"... ]
+               ProviderToProbes providerToProbes;
+               std::vector<DTraceProbeInfo> emptyList;
+               for(std::vector<DTraceProbeInfo>::iterator it = fDtraceProbeSites.begin(); it != fDtraceProbeSites.end(); ++it) {
+                       const char* providerStart = &it->probeName[16];
+                       const char* providerEnd = strchr(providerStart, '$');
+                       if ( providerEnd != NULL ) {
+                               char providerName[providerEnd-providerStart+1];
+                               strlcpy(providerName, providerStart, providerEnd-providerStart+1);
+                               ProviderToProbes::iterator pos = providerToProbes.find(providerName);
+                               if ( pos == providerToProbes.end() ) {
+                                       const char* dup = strdup(providerName);
+                                       providerToProbes[dup] = emptyList;
+                               }
+                               providerToProbes[providerName].push_back(*it);
+                       }
+               }
+               for(std::vector<DTraceProbeInfo>::iterator it = fDtraceIsEnabledSites.begin(); it != fDtraceIsEnabledSites.end(); ++it) {
+                       const char* providerStart = &it->probeName[20];
+                       const char* providerEnd = strchr(providerStart, '$');
+                       if ( providerEnd != NULL ) {
+                               char providerName[providerEnd-providerStart+1];
+                               strlcpy(providerName, providerStart, providerEnd-providerStart+1);
+                               ProviderToProbes::iterator pos = providerToProbes.find(providerName);
+                               if ( pos == providerToProbes.end() ) {
+                                       const char* dup = strdup(providerName);
+                                       providerToProbes[dup] = emptyList;
+                               }
+                               providerToProbes[providerName].push_back(*it);
+                       }
+               }
+               
+               // create a DOF section for each provider
+               int dofIndex=1;
+               CStringSet sectionNamesUsed;
+               for(ProviderToProbes::iterator pit = providerToProbes.begin(); pit != providerToProbes.end(); ++pit, ++dofIndex) {
+                       const char* providerName = pit->first;
+                       const std::vector<DTraceProbeInfo>& probes = pit->second;
+
+                       // open library and find dtrace_create_dof()
+                       void* handle = dlopen("/usr/lib/libdtrace.dylib", RTLD_LAZY);
+                       if ( handle == NULL )
+                               throwf("couldn't dlopen() /usr/lib/libdtrace.dylib: %s\n", dlerror());
+                       createdof_func_t pCreateDOF = (createdof_func_t)dlsym(handle, "dtrace_ld_create_dof");
+                       if ( pCreateDOF == NULL )
+                               throwf("couldn't find \"dtrace_ld_create_dof\" in /usr/lib/libdtrace.dylib: %s\n", dlerror());
+                       // build list of typedefs/stability infos for this provider
+                       CStringSet types;
+                       for(std::vector<DTraceProbeInfo>::const_iterator it = probes.begin(); it != probes.end(); ++it) {
+                               std::map<const ObjectFile::Atom*,CStringSet>::iterator pos = fDtraceAtomToTypes.find(it->atom);
+                               if ( pos != fDtraceAtomToTypes.end() ) {
+                                       for(CStringSet::iterator sit = pos->second.begin(); sit != pos->second.end(); ++sit) {
+                                               const char* providerStart = strchr(*sit, '$')+1;
+                                               const char* providerEnd = strchr(providerStart, '$');
+                                               if ( providerEnd != NULL ) {
+                                                       char aProviderName[providerEnd-providerStart+1];
+                                                       strlcpy(aProviderName, providerStart, providerEnd-providerStart+1);
+                                                       if ( strcmp(aProviderName, providerName) == 0 )
+                                                               types.insert(*sit);
+                                               }
+                                       }
+                               }
+                       }
+                       int typeCount = types.size();
+                       const char* typeNames[typeCount];
+                       //fprintf(stderr, "types for %s:\n", providerName);
+                       uint32_t index = 0;
+                       for(CStringSet::iterator it = types.begin(); it != types.end(); ++it) {
+                               typeNames[index] = *it;
+                               //fprintf(stderr, "\t%s\n", *it);
+                               ++index;
+                       }
+                       
+                       // build list of probe/isenabled sites
+                       const uint32_t probeCount = probes.size();
+                       const char* probeNames[probeCount];
+                       const char* funtionNames[probeCount];
+                       uint64_t offsetsInDOF[probeCount];
+                       index = 0;
+                       for(std::vector<DTraceProbeInfo>::const_iterator it = probes.begin(); it != probes.end(); ++it) {
+                               probeNames[index] = it->probeName;
+                               funtionNames[index] = it->atom->getName();
+                               offsetsInDOF[index] = 0;
+                               ++index;
+                       }
+                       // call dtrace library to create DOF section
+                       size_t dofSectionSize;
+                       uint8_t* p = (*pCreateDOF)(fArchitecture, typeCount, typeNames, probeCount, probeNames, funtionNames, offsetsInDOF, &dofSectionSize);
+                       if ( p != NULL ) {
+                               char sectionName[18];
+                               strcpy(sectionName, "__dof_");
+                               strlcpy(&sectionName[6], providerName, 10);
+                               // create unique section name so each DOF is in its own section
+                               if ( sectionNamesUsed.count(sectionName) != 0 ) {
+                                       sectionName[15] = '0';
+                                       sectionName[16] = '\0';
+                                       while ( sectionNamesUsed.count(sectionName) != 0 )
+                                               ++sectionName[15];
+                               }
+                               sectionNamesUsed.insert(sectionName);
+                               char symbolName[strlen(providerName)+64];
+                               sprintf(symbolName, "__dtrace_dof_for_provider_%s", providerName);
+                               opaque_section::Reader* reader = new opaque_section::Reader("__TEXT", sectionName, 
+                                                                                                               "dtrace", p, dofSectionSize, fNextInputOrdinal, symbolName);
+                               fNextInputOrdinal += dofSectionSize;
+                               // add references
+                               for (uint32_t i=0; i < probeCount; ++i) {
+                                       uint64_t offset = offsetsInDOF[i];
+                                       //fprintf(stderr, "%s offset[%d]=0x%08llX\n", providerName, i, offset);
+                                       if ( offset > dofSectionSize )
+                                               throwf("offsetsInDOF[i]=%0llX > dofSectionSize=%0lX\n", i, offset, dofSectionSize);
+                                       reader->addSectionReference(pcRelKind(fArchitecture), offset, probes[i].atom, probes[i].offset, reader->getAtoms()[0], 0);
+                               }
+                               this->addAtoms(reader->getAtoms());
+                       }
+                       else {
+                               throw "error creating dtrace DOF section";
+                       }
+               }
+       }
+       // create a __DATA __dof section iff -dtrace option was used and static probes were found in .o files
+       else if ( fOptions.dTrace() && (fDtraceProbes.size() != 0) ) {
+               const uint32_t probeCount = fDtraceProbes.size();
+               const char* labels[probeCount];
+               const char* funtionNames[probeCount];
+               uint64_t offsetsInDOF[probeCount];
+
+               // open libray and find dtrace_ld64_create_dof()
+               void* handle = dlopen("/usr/lib/libdtrace.dylib", RTLD_LAZY);
+               if ( handle == NULL )
+                       throwf("couldn't dlopen() /usr/lib/libdtrace.dylib: %s\n", dlerror());
+               oldcreatedof_func_t pCreateDOF = (oldcreatedof_func_t)dlsym(handle, "dtrace_ld64_create_dof");
+               if ( pCreateDOF == NULL )
+                       throwf("couldn't find \"dtrace_ld64_create_dof\" in /usr/lib/libdtrace.dylib: %s\n", dlerror());
+
+               // build argument list
+               uint32_t index = 0;
+               for(std::vector<DTraceProbeInfo>::iterator it = fDtraceProbes.begin(); it != fDtraceProbes.end(); ++it) {
+                       labels[index] = it->probeName;
+                       funtionNames[index] = it->atom->getName();
+                       offsetsInDOF[index] = 0;
+                       ++index;
+               }
+               size_t dofSectionSize;
+               // call dtrace library to create DOF section
+               uint8_t* p = (*pCreateDOF)(fOptions.dTraceScriptName(), fArchitecture, probeCount, labels, funtionNames, offsetsInDOF, &dofSectionSize);
+               if ( p != NULL ) {
+                       opaque_section::Reader* reader = new opaque_section::Reader("__DATA", "__dof", "dtrace", p, dofSectionSize, fNextInputOrdinal);
+                       fNextInputOrdinal += dofSectionSize;
+                       // add references
+                       for (uint32_t i=0; i < probeCount; ++i) {
+                               uint64_t offset = offsetsInDOF[i];
+                               if ( offset > dofSectionSize )
+                                       throwf("offsetsInDOF[i]=%0llX > dofSectionSize=%0lX\n", i, offset, dofSectionSize);
+                               reader->addSectionReference(pointerKind(fArchitecture), offset, fDtraceProbes[i].atom, fDtraceProbes[i].offset);
+                       }
+                       this->addAtoms(reader->getAtoms());
+               }
+               else {
+                       throw "error created dtrace DOF section";
+               }
+       }
+}
+
+
+static bool matchesObjectFile(ObjectFile::Atom* atom, const char* objectFileLeafName)
+{
+       if ( objectFileLeafName == NULL )
+               return true;
+       const char* atomFullPath = atom->getFile()->getPath();
+       const char* lastSlash = strrchr(atomFullPath, '/');
+       if ( lastSlash != NULL ) {
+               if ( strcmp(&lastSlash[1], objectFileLeafName) == 0 )
+                       return true;
+       }
+       else {
+               if ( strcmp(atomFullPath, objectFileLeafName) == 0 )
+                       return true;
+       }
+       return false;
+}
+
+
+static bool usesAnonymousNamespace(const char* symbol)
+{
+       return ( (strncmp(symbol, "__Z", 3) == 0) && (strstr(symbol, "_GLOBAL__N_") != NULL) );
+}
+
+
+//
+//  convert:
+//             __ZN20_GLOBAL__N__Z5main2v3barEv                                        =>  _ZN-3barEv
+//             __ZN37_GLOBAL__N_main.cxx_00000000_493A01A33barEv       =>  _ZN-3barEv
+//
+static void canonicalizeAnonymousName(const char* inSymbol, char outSymbol[])
+{
+       const char* globPtr = strstr(inSymbol, "_GLOBAL__N_");
+       while ( isdigit(*(--globPtr)) )
+               ; // loop
+       char* endptr;
+       unsigned long length = strtoul(globPtr+1, &endptr, 10);
+       const char* globEndPtr = endptr + length;
+       int startLen = globPtr-inSymbol+1;
+       memcpy(outSymbol, inSymbol, startLen);
+       outSymbol[startLen] = '-';
+       strcpy(&outSymbol[startLen+1], globEndPtr);
+}
+
+
+ObjectFile::Atom* Linker::findAtom(const Options::OrderedSymbol& orderedSymbol)
+{
+       ObjectFile::Atom* atom = fGlobalSymbolTable.find(orderedSymbol.symbolName);
+       if ( atom != NULL ) {
+               if ( matchesObjectFile(atom, orderedSymbol.objectFileName) )
+                       return atom;
+       }
+       else {
+               // slow case.  The requested symbol is not in symbol table, so might be static function
+               static SymbolTable::Mapper hashTableOfTranslationUnitScopedSymbols;
+               static SymbolTable::Mapper hashTableOfSymbolsWithAnonymousNamespace;
+               static bool built = false;
+               // build a hash_map the first time
+               if ( !built ) {
+                       for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                               atom = *it;
+                               const char* name = atom->getName();
+                               if ( name != NULL) {
+                                       if ( usesAnonymousNamespace(name) ) {
+                                               // symbol that uses anonymous namespace
+                                               char canonicalName[strlen(name)+2];
+                                               canonicalizeAnonymousName(name, canonicalName);
+                                               const char* hashName = strdup(canonicalName);
+                                               SymbolTable::Mapper::iterator pos = hashTableOfSymbolsWithAnonymousNamespace.find(hashName);
+                                               if ( pos == hashTableOfSymbolsWithAnonymousNamespace.end() )
+                                                       hashTableOfSymbolsWithAnonymousNamespace[hashName] = atom;
+                                               else
+                                                       hashTableOfSymbolsWithAnonymousNamespace[hashName] = NULL;      // collision, denote with NULL
+                                       }
+                                       else if ( atom->getScope() == ObjectFile::Atom::scopeTranslationUnit ) {
+                                               // static function or data
+                                               SymbolTable::Mapper::iterator pos = hashTableOfTranslationUnitScopedSymbols.find(name);
+                                               if ( pos == hashTableOfTranslationUnitScopedSymbols.end() )
+                                                       hashTableOfTranslationUnitScopedSymbols[name] = atom;
+                                               else
+                                                       hashTableOfTranslationUnitScopedSymbols[name] = NULL;   // collision, denote with NULL
+                                       }
+                               }
+                       }
+                       //fprintf(stderr, "built hash table of %lu static functions\n", hashTableOfTranslationUnitScopedSymbols.size());
+                       built = true;
+               }
+
+               // look for name in hashTableOfTranslationUnitScopedSymbols
+               SymbolTable::Mapper::iterator pos = hashTableOfTranslationUnitScopedSymbols.find(orderedSymbol.symbolName);
+               if ( pos != hashTableOfTranslationUnitScopedSymbols.end() ) {
+                       if ( (pos->second != NULL) && matchesObjectFile(pos->second, orderedSymbol.objectFileName) ) {
+                               //fprintf(stderr, "found %s in hash table\n", orderedSymbol.symbolName);
+                               return pos->second;
+                       }
+                       if ( pos->second == NULL )
+                       // name is in hash table, but atom is NULL, so that means there are duplicates, so we use super slow way
+                       for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                               atom = *it;
+                               if ( atom->getScope() == ObjectFile::Atom::scopeTranslationUnit ) {
+                                       const char* name = atom->getName();
+                                       if ( (name != NULL) && (strcmp(name, orderedSymbol.symbolName) == 0) ) {
+                                               if ( matchesObjectFile(atom, orderedSymbol.objectFileName) ) {
+                                                       if ( fOptions.printOrderFileStatistics() )
+                                                               fprintf(stderr, "ld: warning %s specified in order_file but it exists in multiple .o files. "
+                                                                               "Prefix symbol with .o filename in order_file to disambiguate\n", orderedSymbol.symbolName);
+                                                       return atom;
+                                               }
+                                       }
+                               }
+                       }
+               }
+               
+               // look for name in hashTableOfSymbolsWithAnonymousNamespace
+               if ( usesAnonymousNamespace(orderedSymbol.symbolName) ) {
+                       // symbol that uses anonymous namespace
+                       char canonicalName[strlen(orderedSymbol.symbolName)+2];
+                       canonicalizeAnonymousName(orderedSymbol.symbolName, canonicalName);
+                       SymbolTable::Mapper::iterator pos = hashTableOfSymbolsWithAnonymousNamespace.find(canonicalName);
+                       if ( pos != hashTableOfSymbolsWithAnonymousNamespace.end() ) {
+                               if ( (pos->second != NULL) && matchesObjectFile(pos->second, orderedSymbol.objectFileName) ) {
+                                       //fprintf(stderr, "found %s in anonymous namespace hash table\n", canonicalName);
+                                       return pos->second;
+                               }
+                               if ( pos->second == NULL )
+                               // name is in hash table, but atom is NULL, so that means there are duplicates, so we use super slow way
+                               for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                                       atom = *it;
+                                       const char* name = atom->getName();
+                                       if ( (name != NULL) && usesAnonymousNamespace(name) ) {
+                                               char canonicalAtomName[strlen(name)+2];
+                                               canonicalizeAnonymousName(name, canonicalAtomName);
+                                               if ( strcmp(canonicalAtomName, canonicalName) == 0 ) {
+                                                       if ( matchesObjectFile(atom, orderedSymbol.objectFileName) ) {
+                                                               if ( fOptions.printOrderFileStatistics() )
+                                                                       fprintf(stderr, "ld: warning %s specified in order_file but it exists in multiple .o files. "
+                                                                               "Prefix symbol with .o filename in order_file to disambiguate\n", orderedSymbol.symbolName);
+                                                               return atom;
+                                                       }
+                                               }
+                                       }
+                               }
+                       }
+               }
+       }
+       return NULL;
+}
+
+
+void Linker::sortSections()
 {
        Section::assignIndexes();
-       std::sort(fAllAtoms.begin(), fAllAtoms.end(), Linker::AtomSorter());
+}
+
+
+//
+// Linker::sortAtoms()
+//
+// The purpose of this method is to take the graph of all Atoms and produce an ordered
+// sequence of atoms.  The constraints are that: 1) all Atoms of the same Segment must
+// be contiguous, 2)  all Atoms of the same Section must be contigous, 3) Atoms specified
+// in an order_file are seqenced as in the order_file and before Atoms not specified,
+// 4) Atoms in the same section from the same .o file should be contiguous and sequenced
+// in the same order they were in the .o file, 5) Atoms in the same Section but which came
+// from different .o files should be sequenced in the same order that the .o files
+// were passed to the linker (i.e. command line order).
+//
+// The way this is implemented is that the linker passes a "base ordinal" to each Reader
+// as it is constructed.  The reader should construct it Atoms so that calling getOrdinal()
+// on its atoms returns a contiguous range of values starting at the base ordinal.  Then
+// sorting is just sorting by section, then by ordinal.
+//
+// If an order_file is specified, it gets more complicated.  First, an override-ordinal map
+// is created.  It causes the sort routine to ignore the value returned by getOrdinal() and
+// use the override value instead.  Next some Atoms must be layed out consecutively
+// (e.g. hand written assembly that does not end with return, but rather falls into
+// the next label).  This is modeled in Readers via a "kFollowOn" reference.  The use of
+// kFollowOn refernces produces "clusters" of atoms that must stay together.
+// If an order_file tries to move one atom, it may need to move a whole cluster.  The
+// algorithm to do this models clusters using two maps.  The "starts" maps maps any
+// atom in a cluster to the first Atom in the cluster.  The "nexts" maps an Atom in a
+// cluster to the next Atom in the cluster.  With this in place, while processing an
+// order_file, if any entry is in a cluster (in "starts" map), then the entire cluster is
+// given ordinal overrides.
+//
+void Linker::sortAtoms()
+{
+       fStartSortTime = mach_absolute_time();
+       // if -order_file is used, build map of atom ordinal overrides
+       std::map<const ObjectFile::Atom*, uint32_t>* ordinalOverrideMap = NULL;
+       std::map<const ObjectFile::Atom*, uint32_t> theOrdinalOverrideMap;
+       const bool log = false;
+       if ( fOptions.orderedSymbols().size() != 0 ) {
+               // first make a pass to find all follow-on references and build start/next maps
+               // which are a way to represent clusters of atoms that must layout together
+               std::map<const ObjectFile::Atom*, const ObjectFile::Atom*> followOnStarts;
+               std::map<const ObjectFile::Atom*, const ObjectFile::Atom*> followOnNexts;
+               for (std::vector<ObjectFile::Atom*>::iterator ait=fAllAtoms.begin(); ait != fAllAtoms.end(); ait++) {
+                       ObjectFile::Atom* atom = *ait;
+                       std::vector<class ObjectFile::Reference*>& references = atom->getReferences();
+                       for (std::vector<ObjectFile::Reference*>::iterator rit=references.begin(); rit != references.end(); rit++) {
+                               ObjectFile::Reference* ref = *rit;
+                               if ( ref->getKind() == 1 ) {    // FIX FIX
+                                       ObjectFile::Atom* targetAtom = &ref->getTarget();
+                                       if ( log ) fprintf(stderr, "ref %s -> %s", atom->getDisplayName(), targetAtom->getDisplayName());
+                                       std::map<const ObjectFile::Atom*, const ObjectFile::Atom*>::iterator startFrom = followOnStarts.find(atom);
+                                       std::map<const ObjectFile::Atom*, const ObjectFile::Atom*>::iterator startTo = followOnStarts.find(targetAtom);
+                                       if ( (startFrom == followOnStarts.end()) && (startTo == followOnStarts.end()) ) {
+                                               // this is first time we've seen either atom, make simple cluster of the two
+                                               if ( log ) fprintf(stderr, "  new cluster\n");
+                                               followOnStarts[atom] = atom;
+                                               followOnStarts[targetAtom] = atom;
+                                               followOnNexts[atom] = targetAtom;
+                                               followOnNexts[targetAtom] = NULL;
+                                       }
+                                       else if ( (startFrom != followOnStarts.end()) && (startTo == followOnStarts.end()) && (followOnNexts[atom] == NULL) ) {
+                                               // atom is at end of an existing cluster, so append target to end of cluster
+                                               if ( log ) fprintf(stderr, "  end of cluster starting with %s\n", followOnStarts[atom]->getDisplayName());
+                                               followOnNexts[atom] = targetAtom;
+                                               followOnNexts[targetAtom] = NULL;
+                                               followOnStarts[targetAtom] = followOnStarts[atom];
+                                       }
+                                       else {
+                                               // gerneral case of inserting into an existing cluster
+                                               if ( followOnNexts[atom] != NULL ) {
+                                                       // an atom with two follow-ons is illegal
+                                                       fprintf(stderr, "ld: warning can't order %s because both %s and %s must follow it\n",
+                                                                               atom->getDisplayName(), targetAtom->getDisplayName(), followOnNexts[atom]->getDisplayName());
+                                               }
+                                               else {
+                                                       // there already exists an atom that says target must be its follow-on
+                                                       const ObjectFile::Atom* originalStart = startTo->second;
+                                                       const ObjectFile::Atom* originalPrevious = originalStart;
+                                                       while ( followOnNexts[originalPrevious] != targetAtom )
+                                                               originalPrevious = followOnNexts[originalPrevious];
+                                                       bool otherIsAlias = (originalPrevious->getSize() == 0);
+                                                       bool thisIsAlias = (atom->getSize() == 0);
+                                                       if ( !otherIsAlias && !thisIsAlias ) {
+                                                               fprintf(stderr, "ld: warning can't order %s because both %s and %s must preceed it\n",
+                                                                                       targetAtom->getDisplayName(), originalPrevious->getDisplayName(), atom->getDisplayName());
+                                                       }
+                                                       else if ( otherIsAlias ) {
+                                                               if ( originalPrevious == originalStart ) {
+                                                                       // other is alias at start of cluster, make this the new start of cluster
+                                                                       if ( log ) fprintf(stderr, "  becomes new start of cluster previous starting with %s\n", originalStart->getDisplayName());
+                                                                       followOnNexts[atom] = originalPrevious;
+                                                                       for(const ObjectFile::Atom* nextAtom = atom; nextAtom != NULL; nextAtom = followOnNexts[nextAtom])
+                                                                               followOnStarts[nextAtom] = atom;
+                                                               }
+                                                               else {
+                                                                       // other is alias in middle of cluster, insert new atom before it
+                                                                       if ( log ) fprintf(stderr, "  insert into cluster starting with %s before alias %s\n", originalStart->getDisplayName(), originalPrevious->getDisplayName());
+                                                                       followOnStarts[atom] = originalStart;
+                                                                       followOnNexts[atom] = originalPrevious;
+                                                                       for(const ObjectFile::Atom* a = originalStart; a != NULL; a = followOnNexts[a]) {
+                                                                               if ( followOnNexts[a] == originalPrevious ) {
+                                                                                       followOnNexts[a] = atom;
+                                                                                       break;
+                                                                               }
+                                                                       }
+                                                               }
+                                                       }
+                                                       else {
+                                                               // this is alias, so it can go inbetween originalPrevious and targetAtom
+                                                               if ( log ) fprintf(stderr, "  insert into cluster starting with %s after %s\n", originalStart->getDisplayName(), originalPrevious->getDisplayName());
+                                                               followOnStarts[atom] = originalStart;
+                                                               followOnNexts[atom] = followOnNexts[originalPrevious];
+                                                               followOnNexts[originalPrevious] = atom;
+                                                       }
+                                               }
+                                       }
+                               }
+                       }
+               }
+
+               if ( log ) {
+                       for(std::map<const ObjectFile::Atom*, const ObjectFile::Atom*>::iterator it = followOnStarts.begin(); it != followOnStarts.end(); ++it)
+                               fprintf(stderr, "start %s -> %s\n", it->first->getDisplayName(), it->second->getDisplayName());
+
+                       for(std::map<const ObjectFile::Atom*, const ObjectFile::Atom*>::iterator it = followOnNexts.begin(); it != followOnNexts.end(); ++it)
+                               fprintf(stderr, "next %s -> %s\n", it->first->getDisplayName(), (it->second != NULL) ? it->second->getDisplayName() : "null");
+               }
+
+               // with the start/next maps of follow-on atoms we can process the order file and produce override ordinals
+               ordinalOverrideMap = &theOrdinalOverrideMap;
+               uint32_t index = 0;
+               uint32_t matchCount = 0;
+               std::vector<Options::OrderedSymbol>& orderedSymbols = fOptions.orderedSymbols();
+               for(std::vector<Options::OrderedSymbol>::iterator it = orderedSymbols.begin(); it != orderedSymbols.end(); ++it) {
+                       ObjectFile::Atom* atom = this->findAtom(*it);
+                       if ( atom != NULL ) {
+                               std::map<const ObjectFile::Atom*, const ObjectFile::Atom*>::iterator start = followOnStarts.find(atom);
+                               if ( start != followOnStarts.end() ) {
+                                       // this symbol for the order file corresponds to an atom that is in a cluster that must lay out together
+                                       for(const ObjectFile::Atom* nextAtom = start->second; nextAtom != NULL; nextAtom = followOnNexts[nextAtom]) {
+                                               std::map<const ObjectFile::Atom*, uint32_t>::iterator pos = theOrdinalOverrideMap.find(nextAtom);
+                                               if ( pos == theOrdinalOverrideMap.end() ) {
+                                                       theOrdinalOverrideMap[nextAtom] = index++;
+                                                       if (log ) fprintf(stderr, "override ordinal %u assigned to %s in cluster from %s\n", index, nextAtom->getDisplayName(), nextAtom->getFile()->getPath());
+                                               }
+                                               else {
+                                                       if (log ) fprintf(stderr, "could not order %s as %u because it was already laid out earlier by %s as %u\n",
+                                                                                       atom->getDisplayName(), index, followOnStarts[atom]->getDisplayName(), theOrdinalOverrideMap[atom] );
+                                               }
+                                       }
+                               }
+                               else {
+                                       theOrdinalOverrideMap[atom] = index;
+                                       if (log ) fprintf(stderr, "override ordinal %u assigned to %s from %s\n", index, atom->getDisplayName(), atom->getFile()->getPath());
+                               }
+                       }
+                       else {
+                               ++matchCount;
+                               //fprintf(stderr, "can't find match for order_file entry %s/%s\n", it->objectFileName, it->symbolName);
+                       }
+                        ++index;
+               }
+               if ( fOptions.printOrderFileStatistics() && (fOptions.orderedSymbols().size() != matchCount) ) {
+                       fprintf(stderr, "ld: warning only %u out of %lu order_file symbols were applicable\n", matchCount, fOptions.orderedSymbols().size() );
+               }
+       }
+
+       // sort atoms
+       std::sort(fAllAtoms.begin(), fAllAtoms.end(), Linker::AtomSorter(ordinalOverrideMap));
+
        //fprintf(stderr, "Sorted atoms:\n");
        //for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
-       //      fprintf(stderr, "\t%s\n", (*it)->getDisplayName());
+       //      fprintf(stderr, "\t%p, %u  %s\n", (*it)->getSection(), (*it)->getSection()->getIndex(), (*it)->getDisplayName());
        //}
 }
 
 
-
 // make sure given addresses are within reach of branches, etc
 void Linker::tweakLayout()
 {
+       // > 2GB images need their large zero fill atoms sorted to the end to keep access with +/- 2GB
+       if ( fTotalSize > 0x7F000000 ) {
+               fBiggerThanTwoGigOutput = true;
+
+               if ( (fTotalSize-fTotalZeroFillSize) > 0x7F000000 )
+                       throwf("total output size exceeds 2GB (%lldMB)", (fTotalSize-fTotalZeroFillSize)/(1024*1024));          
+
+               // move very large (>1MB) zero fill atoms to a new section at very end
+               Section* hugeZeroFills = Section::find("__huge", "__DATA", true);
+               for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                       ObjectFile::Atom* atom = *it;
+                       if ( atom->isZeroFill() && (atom->getSize() > 1024*1024) && atom->getSegment().isContentReadable() )
+                               atom->setSection(hugeZeroFills);
+               }
+       }
 }
 
-void Linker::writeOutput()
+
+void Linker::writeDotOutput()
+{
+       const char* dotOutFilePath = fOptions.dotOutputFile();
+       if ( dotOutFilePath != NULL ) {
+               FILE* out = fopen(dotOutFilePath, "w");
+               if ( out != NULL ) {
+                       // print header
+                       fprintf(out, "digraph dg\n{\n");
+                       fprintf(out, "\tconcentrate = true;\n");
+                       fprintf(out, "\trankdir = LR;\n");
+
+                       // print each atom as a node
+                       for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                               ObjectFile::Atom* atom = *it;
+                               if ( atom->getFile() != fOutputFile ) {
+                                       const char* name = atom->getDisplayName();
+                                       if ( (atom->getDefinitionKind() == ObjectFile::Atom::kExternalDefinition)
+                                         || (atom->getDefinitionKind() == ObjectFile::Atom::kExternalWeakDefinition) ) {
+                                               fprintf(out, "\taddr%p [ shape = plaintext, label = \"%s\" ];\n", atom, name);
+                                       }
+                                       else if ( strcmp(atom->getSectionName(), "__cstring") == 0 ) {
+                                               char cstring[atom->getSize()+2];
+                                               atom->copyRawContent((uint8_t*)cstring);
+                                               fprintf(out, "\taddr%p [ label = \"string: '", atom);
+                                               for (const char* s=cstring; *s != '\0'; ++s) {
+                                                       if ( *s == '\n' )
+                                                               fprintf(out, "\\\\n");
+                                                       else
+                                                               fputc(*s, out);
+                                               }
+                                               fprintf(out, "'\" ];\n");
+                                       }
+                                       else {
+                                               fprintf(out, "\taddr%p [ label = \"%s\" ];\n", atom, name);
+                                       }
+                               }
+                       }
+                       fprintf(out, "\n");
+
+                       // print each reference as an edge
+                       for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                               ObjectFile::Atom* fromAtom = *it;
+                               if ( fromAtom->getFile() != fOutputFile ) {
+                                       std::vector<ObjectFile::Reference*>&  references = fromAtom->getReferences();
+                                       std::set<ObjectFile::Atom*> seenTargets;
+                                       for (std::vector<ObjectFile::Reference*>::iterator rit=references.begin(); rit != references.end(); rit++) {
+                                               ObjectFile::Reference* reference = *rit;
+                                               ObjectFile::Atom* toAtom = &(reference->getTarget());
+                                               if ( seenTargets.count(toAtom) == 0 ) {
+                                                       seenTargets.insert(toAtom);
+                                                       fprintf(out, "\taddr%p -> addr%p;\n", fromAtom, toAtom);
+                                               }
+                                       }
+                               }
+                       }
+                       fprintf(out, "\n");
+
+                       // push all imports to bottom of graph
+                       fprintf(out, "{ rank = same; ");
+                       for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                               ObjectFile::Atom* atom = *it;
+                               if ( atom->getFile() != fOutputFile )
+                                       if ( (atom->getDefinitionKind() == ObjectFile::Atom::kExternalDefinition)
+                                         || (atom->getDefinitionKind() == ObjectFile::Atom::kExternalWeakDefinition) ) {
+                                               fprintf(out, "addr%p; ", atom);
+                                       }
+                       }
+                       fprintf(out, "};\n ");
+
+                       // print footer
+                       fprintf(out, "}\n");
+                       fclose(out);
+               }
+               else {
+                       fprintf(stderr, "ld: warning could not write dot output file: %s\n", dotOutFilePath);
+               }
+       }
+}
+
+ObjectFile::Atom* Linker::entryPoint()
 {
        // if main executable, find entry point atom
        ObjectFile::Atom* entryPoint = NULL;
@@ -781,14 +2014,14 @@ void Linker::writeOutput()
                case Options::kDyld:
                        entryPoint = fGlobalSymbolTable.find(fOptions.entryName());
                        if ( entryPoint == NULL ) {
-                               throwf("could not find entry point: %s", fOptions.entryName());
+                               throwf("could not find entry point \"%s\" (perhaps missing crt1.o)", fOptions.entryName());
                        }
                        break;
                case Options::kDynamicLibrary:
                        if ( fOptions.initFunctionName() != NULL ) {
                                entryPoint = fGlobalSymbolTable.find(fOptions.initFunctionName());
                                if ( entryPoint == NULL ) {
-                                       throwf("could not find -init function: %s", fOptions.initFunctionName());
+                                       throwf("could not find -init function: \"%s\"", fOptions.initFunctionName());
                                }
                        }
                        break;
@@ -797,13 +2030,669 @@ void Linker::writeOutput()
                        entryPoint = NULL;
                        break;
        }
-       
-       // tell writer about each segment's atoms
-       fOutputFile->write(fAllAtoms, entryPoint);
+       return entryPoint;
+}
+
+ObjectFile::Atom* Linker::dyldHelper()
+{
+       return fGlobalSymbolTable.find("dyld_stub_binding_helper");
+}
+
+const char* Linker::assureFullPath(const char* path)
+{
+       if ( path[0] == '/' )
+               return path;
+       char cwdbuff[MAXPATHLEN];
+       if ( getcwd(cwdbuff, MAXPATHLEN) != NULL ) {
+               char* result;
+               asprintf(&result, "%s/%s", cwdbuff, path);
+               if ( result != NULL )
+                       return result;
+       }
+       return path;
+}
+
+
+//
+// The stab strings are of the form:
+//             <name> ':' <type-code> <number-pari>
+//  but the <name> contain a colon.
+//  For C++ <name> may contain a double colon (e.g. std::string:f(0,1) )
+//  For Objective-C name may contain a colon instead square bracket (e.g. [Foo doit:]:f(0,1) )
+//
+const char* Linker::truncateStabString(const char* str)
+{
+       enum { start, inObjc } state = start;
+       for (const char* s = str; *s != 0; ++s) {
+               char c = *s;
+               switch (state) {
+                       case start:
+                               if ( c == '[' ) {
+                                       state = inObjc;
+                               }
+                               else {
+                                       if ( c == ':' ) {
+                                               if ( s[1] == ':' ) {
+                                                       ++s;
+                                               }
+                                               else {
+                                                       // found colon
+                                                       // Duplicate strndup behavior here.
+                                                       int trunStrLen = s-str+2;
+                                                       char* temp = new char[trunStrLen+1];
+                                                       memcpy(temp, str, trunStrLen);
+                                                       temp[trunStrLen] = '\0';
+                                                       return temp;
+                                               }
+                                       }
+                               }
+                               break;
+                       case inObjc:
+                               if ( c == ']' ) {
+                                       state = start;
+                               }
+                               break;
+               }
+       }
+       // malformed
+       return str;
+}
+
+
+bool Linker::minimizeStab(ObjectFile::Reader::Stab& stab)
+{
+       switch(stab.type){
+               case N_GSYM:
+               case N_STSYM:
+               case N_LCSYM:
+               case N_FUN:
+                       // these all need truncated strings
+                       stab.string = truncateStabString(stab.string);
+                       return true;
+               case N_SO:
+               case N_OSO:
+               case N_OPT:
+               case N_SOL:
+                       // these are included in the minimal stabs, but they keep their full string
+                       return true;
+               default:
+                       return false;
+       }
+}
+
+
+struct HeaderRange {
+       std::vector<ObjectFile::Reader::Stab>::iterator begin;
+       std::vector<ObjectFile::Reader::Stab>::iterator end;
+       int                                                                                             parentRangeIndex;
+       uint32_t                                                                                sum;
+       bool                                                                                    sumPrecomputed;
+       bool                                                                                    useEXCL;
+       bool                                                                                    cannotEXCL; // because of SLINE, etc stabs
+};
+
+
+typedef __gnu_cxx::hash_map<const char*, std::vector<uint32_t>, __gnu_cxx::hash<const char*>, CStringEquals> PathToSums;
+
+// hash table that maps header path to a vector of known checksums for that path
+static PathToSums sKnownBINCLs;
+
+
+void Linker::collectStabs(ObjectFile::Reader* reader, std::map<const class ObjectFile::Atom*, uint32_t>& atomOrdinals)
+{
+       bool log = false;
+       bool minimal = ( fOptions.readerOptions().fDebugInfoStripping == ObjectFile::ReaderOptions::kDebugInfoMinimal );
+       std::vector<class ObjectFile::Reader::Stab>* readerStabs = reader->getStabs();
+       if ( readerStabs == NULL )
+               return;
+
+       if ( log ) fprintf(stderr, "processesing %lu stabs for %s\n", readerStabs->size(), reader->getPath());
+       std::vector<HeaderRange> ranges;
+       int curRangeIndex = -1;
+       int count = 0;
+       ObjectFile::Atom* atomWithLowestOrdinal = NULL;
+       ObjectFile::Atom* atomWithHighestOrdinal = NULL;
+       uint32_t highestOrdinal = 0;
+       uint32_t lowestOrdinal = UINT_MAX;
+       std::vector<std::pair<ObjectFile::Atom*,ObjectFile::Atom*> > soRanges;
+       // 1) find all (possibly nested) BINCL/EINCL ranges and their checksums
+       // 2) find all SO/SO ranges and the first/last atom own by a FUN stab therein
+       for(std::vector<class ObjectFile::Reader::Stab>::iterator it=readerStabs->begin(); it != readerStabs->end(); ++it) {
+               ++count;
+               switch ( it->type ) {
+                       case N_BINCL:
+                               {
+                                       HeaderRange range;
+                                       range.begin = it;
+                                       range.end = readerStabs->end();
+                                       range.parentRangeIndex = curRangeIndex;
+                                       range.sum = it->value;
+                                       range.sumPrecomputed = (range.sum != 0);
+                                       range.useEXCL = false;
+                                       range.cannotEXCL = false;
+                                       curRangeIndex = ranges.size();
+                                       if ( log ) fprintf(stderr, "[%d]BINCL %s\n", curRangeIndex, it->string);
+                                       ranges.push_back(range);
+                               }
+                               break;
+                       case N_EINCL:
+                               if ( curRangeIndex == -1 ) {
+                                       fprintf(stderr, "ld: warning EINCL missing BINCL in %s\n", reader->getPath());
+                               }
+                               else {
+                                       ranges[curRangeIndex].end = it+1;
+                                       if ( log ) fprintf(stderr, "[%d->%d]EINCL %s\n", curRangeIndex, ranges[curRangeIndex].parentRangeIndex, it->string);
+                                       curRangeIndex = ranges[curRangeIndex].parentRangeIndex;
+                               }
+                               break;
+                       case N_FUN:
+                               {
+                                       std::map<const class ObjectFile::Atom*, uint32_t>::iterator pos = atomOrdinals.find(it->atom);
+                                       if ( pos != atomOrdinals.end() ) {
+                                               uint32_t ordinal = pos->second;
+                                               if ( ordinal > highestOrdinal ) {
+                                                       highestOrdinal = ordinal;
+                                                       atomWithHighestOrdinal = it->atom;
+                                               }
+                                               if ( ordinal < lowestOrdinal ) {
+                                                       lowestOrdinal = ordinal;
+                                                       atomWithLowestOrdinal = it->atom;
+                                               }
+                                       }
+                               }
+                               // fall through
+                       case N_BNSYM:
+                       case N_ENSYM:
+                       case N_LBRAC:
+                       case N_RBRAC:
+                       case N_SLINE:
+                       case N_STSYM:
+                       case N_LCSYM:
+                               if ( curRangeIndex != -1 ) {
+                                       ranges[curRangeIndex].cannotEXCL = true;
+                                       if ( fOptions.warnStabs() )
+                                               fprintf(stderr, "ld: cannot do BINCL/EINCL optimzation because of stabs kinds in %s for %s\n", ranges[curRangeIndex].begin->string, reader->getPath());
+                               }
+                               break;
+                       case N_SO:
+                               if ( (it->string != NULL) && (strlen(it->string) > 0) ) {
+                                       // start SO, reset hi/low FUN tracking
+                                       atomWithLowestOrdinal = NULL;
+                                       atomWithHighestOrdinal = NULL;
+                                       highestOrdinal = 0;
+                                       lowestOrdinal = UINT_MAX;
+                               }
+                               else {
+                                       // end SO, record hi/low atoms for this SO range
+                                       soRanges.push_back(std::make_pair<ObjectFile::Atom*,ObjectFile::Atom*>(atomWithLowestOrdinal, atomWithHighestOrdinal));
+                               }
+                               // fall through
+                       default:
+                               if ( curRangeIndex != -1 ) {
+                                       if ( ! ranges[curRangeIndex].sumPrecomputed ) {
+                                               uint32_t sum = 0;
+                                               const char* s = it->string;
+                                               char c;
+                                               while ( (c = *s++) != 0 ) {
+                                                       sum += c;
+                                                       // don't checkusm first number (file index) after open paren in string
+                                                       if ( c == '(' ) {
+                                                               while(isdigit(*s))
+                                                                       ++s;
+                                                       }
+                                               }
+                                               ranges[curRangeIndex].sum += sum;
+                                       }
+                               }
+
+               }
+       }
+       if ( log ) fprintf(stderr, "processesed %d stabs for %s\n", count, reader->getPath());
+       if ( curRangeIndex != -1 )
+               fprintf(stderr, "ld: warning BINCL (%s) missing EINCL in %s\n", ranges[curRangeIndex].begin->string, reader->getPath());
+
+       // if no BINCLs
+       if ( ranges.size() == 0 ) {
+               int soIndex = 0;
+               for(std::vector<ObjectFile::Reader::Stab>::iterator it=readerStabs->begin(); it != readerStabs->end(); ++it) {
+                       // copy minimal or all stabs
+                       ObjectFile::Reader::Stab stab = *it;
+                       if ( !minimal || minimizeStab(stab) ) {
+                               if ( stab.type == N_SO ) {
+                                       if ( (stab.string != NULL) && (strlen(stab.string) > 0) ) {
+                                               // starting SO is associated with first atom
+                                               stab.atom = soRanges[soIndex].first;
+                                       }
+                                       else {
+                                               // ending SO is associated with last atom
+                                               stab.atom = soRanges[soIndex].second;
+                                               ++soIndex;
+                                       }
+                               }
+                               fStabs.push_back(stab);
+                       }
+               }
+               return;
+       }
+
+       //fprintf(stderr, "BINCL/EINCL info for %s\n", reader->getPath());
+       //for(std::vector<HeaderRange>::iterator it=ranges.begin(); it != ranges.end(); ++it) {
+       //      fprintf(stderr, "%08X %s\n", it->sum, it->begin->string);
+       //}
+
+       // see if any of these BINCL/EINCL ranges have already been seen and therefore can be replaced with EXCL
+       for(std::vector<HeaderRange>::iterator it=ranges.begin(); it != ranges.end(); ++it) {
+               if ( ! it->cannotEXCL ) {
+                       const char* header = it->begin->string;
+                       uint32_t sum = it->sum;
+                       PathToSums::iterator pos = sKnownBINCLs.find(header);
+                       if ( pos != sKnownBINCLs.end() ) {
+                               std::vector<uint32_t>& sums = pos->second;
+                               for(std::vector<uint32_t>::iterator sit=sums.begin(); sit != sums.end(); ++sit) {
+                                       if (*sit == sum) {
+                                               //fprintf(stderr, "use EXCL for %s in %s\n", header, reader->getPath());
+                                               it->useEXCL = true;
+                                               break;
+                                       }
+                               }
+                               if ( ! it->useEXCL ) {
+                                       // have seen this path, but not this checksum
+                                       //fprintf(stderr, "registering another checksum %08X for %s\n", sum, header);
+                                       sums.push_back(sum);
+                               }
+                       }
+                       else {
+                               // have not seen this path, so add to known BINCLs
+                               std::vector<uint32_t> empty;
+                               sKnownBINCLs[header] = empty;
+                               sKnownBINCLs[header].push_back(sum);
+                               //fprintf(stderr, "registering checksum %08X for %s\n", sum, header);
+                       }
+               }
+       }
+
+       // add a new set of stabs with BINCL/EINCL runs that have been seen before, replaced with EXCLs
+       curRangeIndex = -1;
+       const int maxRangeIndex = ranges.size();
+       int soIndex = 0;
+       for(std::vector<ObjectFile::Reader::Stab>::iterator it=readerStabs->begin(); it != readerStabs->end(); ++it) {
+               switch ( it->type ) {
+                       case N_BINCL:
+                               for(int i=curRangeIndex+1; i < maxRangeIndex; ++i) {
+                                       if ( ranges[i].begin == it ) {
+                                               curRangeIndex = i;
+                                               HeaderRange& range = ranges[curRangeIndex];
+                                               ObjectFile::Reader::Stab stab = *it;
+                                               stab.value = range.sum; // BINCL and EXCL have n_value set to checksum
+                                               if ( range.useEXCL )
+                                                       stab.type = N_EXCL;     // transform BINCL into EXCL
+                                               if ( !minimal )
+                                                       fStabs.push_back(stab);
+                                               break;
+                                       }
+                               }
+                               break;
+                       case N_EINCL:
+                               if ( curRangeIndex != -1 ) {
+                                       if ( !ranges[curRangeIndex].useEXCL && !minimal )
+                                               fStabs.push_back(*it);
+                                       curRangeIndex = ranges[curRangeIndex].parentRangeIndex;
+                               }
+                               break;
+                       default:
+                               if ( (curRangeIndex == -1) || !ranges[curRangeIndex].useEXCL ) {
+                                       ObjectFile::Reader::Stab stab = *it;
+                                       if ( !minimal || minimizeStab(stab) ) {
+                                               if ( stab.type == N_SO ) {
+                                                       if ( (stab.string != NULL) && (strlen(stab.string) > 0) ) {
+                                                               // starting SO is associated with first atom
+                                                               stab.atom = soRanges[soIndex].first;
+                                                       }
+                                                       else {
+                                                               // ending SO is associated with last atom
+                                                               stab.atom = soRanges[soIndex].second;
+                                                               ++soIndex;
+                                                       }
+                                               }
+                                               fStabs.push_back(stab);
+                                       }
+                               }
+               }
+       }
+
 }
 
 
+// used to prune out atoms that don't need debug notes generated
+class NoDebugNoteAtom
+{
+public:
+       NoDebugNoteAtom(const std::map<class ObjectFile::Reader*, uint32_t>& readersWithDwarfOrdinals)
+                       : fReadersWithDwarfOrdinals(readersWithDwarfOrdinals) {}
+
+       bool operator()(const ObjectFile::Atom* atom) const {
+               if ( atom->getSymbolTableInclusion() == ObjectFile::Atom::kSymbolTableNotIn )
+                       return true;
+               if ( atom->getName() == NULL )
+                       return true;
+               if ( fReadersWithDwarfOrdinals.find(atom->getFile()) == fReadersWithDwarfOrdinals.end() )
+                       return true;
+               return false;
+       }
+
+private:
+       const std::map<class ObjectFile::Reader*, uint32_t>& fReadersWithDwarfOrdinals;
+};
+
+// used to sort atoms with debug notes
+class ReadersWithDwarfSorter
+{
+public:
+       ReadersWithDwarfSorter(const std::map<class ObjectFile::Reader*, uint32_t>& readersWithDwarfOrdinals,
+                                                  const std::map<const class ObjectFile::Atom*, uint32_t>& atomOrdinals)
+                       : fReadersWithDwarfOrdinals(readersWithDwarfOrdinals), fAtomOrdinals(atomOrdinals) {}
+
+       bool operator()(const ObjectFile::Atom* left, const ObjectFile::Atom* right) const
+       {
+               // first sort by reader
+               unsigned int leftReaderIndex  = fReadersWithDwarfOrdinals.find(left->getFile())->second;
+               unsigned int rightReaderIndex = fReadersWithDwarfOrdinals.find(right->getFile())->second;
+               if ( leftReaderIndex != rightReaderIndex )
+                       return (leftReaderIndex < rightReaderIndex);
+
+               // then sort by atom ordinal
+               unsigned int leftAtomIndex  = fAtomOrdinals.find(left)->second;
+               unsigned int rightAtomIndex = fAtomOrdinals.find(right)->second;
+               return leftAtomIndex < rightAtomIndex;
+       }
 
+private:
+       const std::map<class ObjectFile::Reader*, uint32_t>& fReadersWithDwarfOrdinals;
+       const std::map<const class ObjectFile::Atom*, uint32_t>& fAtomOrdinals;
+};
+
+
+
+
+
+void Linker::synthesizeDebugNotes(std::vector<class ObjectFile::Atom*>& allAtomsByReader)
+{
+       // synthesize "debug notes" and add them to master stabs vector
+       const char* dirPath = NULL;
+       const char* filename = NULL;
+       bool wroteStartSO = false;
+       bool useZeroOSOModTime = (getenv("RC_RELEASE") != NULL);
+       __gnu_cxx::hash_set<const char*, __gnu_cxx::hash<const char*>, CStringEquals>  seenFiles;
+       for (std::vector<ObjectFile::Atom*>::iterator it=allAtomsByReader.begin(); it != allAtomsByReader.end(); it++) {
+               ObjectFile::Atom* atom = *it;
+               const char* newDirPath;
+               const char* newFilename;
+               //fprintf(stderr, "debug note for %s\n", atom->getDisplayName());
+               if ( atom->getTranslationUnitSource(&newDirPath, &newFilename) ) {
+                       // need SO's whenever the translation unit source file changes
+                       if ( newFilename != filename ) {
+                               // gdb like directory SO's to end in '/', but dwarf DW_AT_comp_dir usually does not have trailing '/'
+                               if ( (newDirPath != NULL) && (strlen(newDirPath) > 1 ) && (newDirPath[strlen(newDirPath)-1] != '/') )
+                                       asprintf((char**)&newDirPath, "%s/", newDirPath);
+                               if ( filename != NULL ) {
+                                       // translation unit change, emit ending SO
+                                       ObjectFile::Reader::Stab endFileStab;
+                                       endFileStab.atom                = NULL;
+                                       endFileStab.type                = N_SO;
+                                       endFileStab.other               = 1;
+                                       endFileStab.desc                = 0;
+                                       endFileStab.value               = 0;
+                                       endFileStab.string              = "";
+                                       fStabs.push_back(endFileStab);
+                               }
+                               // new translation unit, emit start SO's
+                               ObjectFile::Reader::Stab dirPathStab;
+                               dirPathStab.atom                = NULL;
+                               dirPathStab.type                = N_SO;
+                               dirPathStab.other               = 0;
+                               dirPathStab.desc                = 0;
+                               dirPathStab.value               = 0;
+                               dirPathStab.string              = newDirPath;
+                               fStabs.push_back(dirPathStab);
+                               ObjectFile::Reader::Stab fileStab;
+                               fileStab.atom           = NULL;
+                               fileStab.type           = N_SO;
+                               fileStab.other          = 0;
+                               fileStab.desc           = 0;
+                               fileStab.value          = 0;
+                               fileStab.string         = newFilename;
+                               fStabs.push_back(fileStab);
+                               // Synthesize OSO for start of file
+                               ObjectFile::Reader::Stab objStab;
+                               objStab.atom            = NULL;
+                               objStab.type            = N_OSO;
+                               objStab.other           = 0;
+                               objStab.desc            = 1;
+                               objStab.value           = useZeroOSOModTime ? 0 : atom->getFile()->getModificationTime();
+                               objStab.string          = assureFullPath(atom->getFile()->getPath());
+                               fStabs.push_back(objStab);
+                               wroteStartSO = true;
+                               // add the source file path to seenFiles so it does not show up in SOLs
+                               seenFiles.insert(newFilename);
+                       }
+                       filename = newFilename;
+                       dirPath = newDirPath;
+                       if ( atom->getSegment().isContentExecutable() && (strncmp(atom->getSectionName(), "__text", 6) == 0) ) {
+                               // Synthesize BNSYM and start FUN stabs
+                               ObjectFile::Reader::Stab beginSym;
+                               beginSym.atom           = atom;
+                               beginSym.type           = N_BNSYM;
+                               beginSym.other          = 1;
+                               beginSym.desc           = 0;
+                               beginSym.value          = 0;
+                               beginSym.string         = "";
+                               fStabs.push_back(beginSym);
+                               ObjectFile::Reader::Stab startFun;
+                               startFun.atom           = atom;
+                               startFun.type           = N_FUN;
+                               startFun.other          = 1;
+                               startFun.desc           = 0;
+                               startFun.value          = 0;
+                               startFun.string         = atom->getName();
+                               fStabs.push_back(startFun);
+                               // Synthesize any SOL stabs needed
+                               std::vector<ObjectFile::LineInfo>* lineInfo = atom->getLineInfo();
+                               if ( lineInfo != NULL ) {
+                                       const char* curFile = NULL;
+                                       for (std::vector<ObjectFile::LineInfo>::iterator it = lineInfo->begin(); it != lineInfo->end(); ++it) {
+                                               if ( it->fileName != curFile ) {
+                                                       if ( seenFiles.count(it->fileName) == 0 ) {
+                                                               seenFiles.insert(it->fileName);
+                                                               ObjectFile::Reader::Stab sol;
+                                                               sol.atom                = 0;
+                                                               sol.type                = N_SOL;
+                                                               sol.other               = 0;
+                                                               sol.desc                = 0;
+                                                               sol.value               = 0;
+                                                               sol.string              = it->fileName;
+                                                               fStabs.push_back(sol);
+                                                       }
+                                                       curFile = it->fileName;
+                                               }
+                                       }
+                               }
+                               // Synthesize end FUN and ENSYM stabs
+                               ObjectFile::Reader::Stab endFun;
+                               endFun.atom                     = atom;
+                               endFun.type                     = N_FUN;
+                               endFun.other            = 0;
+                               endFun.desc                     = 0;
+                               endFun.value            = 0;
+                               endFun.string           = "";
+                               fStabs.push_back(endFun);
+                               ObjectFile::Reader::Stab endSym;
+                               endSym.atom                     = atom;
+                               endSym.type                     = N_ENSYM;
+                               endSym.other            = 1;
+                               endSym.desc                     = 0;
+                               endSym.value            = 0;
+                               endSym.string           = "";
+                               fStabs.push_back(endSym);
+                       }
+                       else {
+                               ObjectFile::Reader::Stab globalsStab;
+                               if ( atom->getScope() == ObjectFile::Atom::scopeTranslationUnit ) {
+                                       // Synthesize STSYM stab for statics
+                                       const char* name = atom->getName();
+                                       if ( name[0] == '_' ) {
+                                               globalsStab.atom                = atom;
+                                               globalsStab.type                = N_STSYM;
+                                               globalsStab.other               = 1;
+                                               globalsStab.desc                = 0;
+                                               globalsStab.value               = 0;
+                                               globalsStab.string              = name;
+                                               fStabs.push_back(globalsStab);
+                                       }
+                               }
+                               else {
+                                       // Synthesize GSYM stab for other globals (but not .eh exception frame symbols)
+                                       const char* name = atom->getName();
+                                       if ( (name[0] == '_') && (strcmp(atom->getSectionName(), "__eh_frame") != 0) ) {
+                                               globalsStab.atom                = atom;
+                                               globalsStab.type                = N_GSYM;
+                                               globalsStab.other               = 1;
+                                               globalsStab.desc                = 0;
+                                               globalsStab.value               = 0;
+                                               globalsStab.string              = name;
+                                               fStabs.push_back(globalsStab);
+                                       }
+                               }
+                       }
+               }
+       }
+
+       if ( wroteStartSO ) {
+               //  emit ending SO
+               ObjectFile::Reader::Stab endFileStab;
+               endFileStab.atom                = NULL;
+               endFileStab.type                = N_SO;
+               endFileStab.other               = 1;
+               endFileStab.desc                = 0;
+               endFileStab.value               = 0;
+               endFileStab.string              = "";
+               fStabs.push_back(endFileStab);
+       }
+}
+
+
+
+
+void Linker::collectDebugInfo()
+{
+       std::map<const class ObjectFile::Atom*, uint32_t>       atomOrdinals;
+       fStartDebugTime = mach_absolute_time();
+       if ( fOptions.readerOptions().fDebugInfoStripping != ObjectFile::ReaderOptions::kDebugInfoNone ) {
+
+               // determine mixture of stabs and dwarf
+               bool someStabs = false;
+               bool someDwarf = false;
+               for (std::vector<class ObjectFile::Reader*>::iterator it=fReadersThatHaveSuppliedAtoms.begin();
+                               it != fReadersThatHaveSuppliedAtoms.end();
+                               it++) {
+                       ObjectFile::Reader* reader = *it;
+                       if ( reader != NULL ) {
+                               switch ( reader->getDebugInfoKind() ) {
+                                       case ObjectFile::Reader::kDebugInfoNone:
+                                               break;
+                                       case ObjectFile::Reader::kDebugInfoStabs:
+                                               someStabs = true;
+                                               break;
+                                       case ObjectFile::Reader::kDebugInfoDwarf:
+                                               someDwarf = true;
+                                               fCreateUUID = true;
+                                               break;
+                                   case ObjectFile::Reader::kDebugInfoStabsUUID:
+                                               someStabs = true;
+                                               fCreateUUID = true;
+                                               break;
+                                       default:
+                                               throw "Unhandled type of debug information";
+                               }
+                       }
+               }
+
+               if ( someDwarf || someStabs ) {
+                       // try to minimize re-allocations
+                       fStabs.reserve(1024);
+
+                       // make mapping from atoms to ordinal
+                       uint32_t ordinal = 1;
+                       for (std::vector<ObjectFile::Atom*>::iterator it=fAllAtoms.begin(); it != fAllAtoms.end(); it++) {
+                               atomOrdinals[*it] = ordinal++;
+                       }
+               }
+
+               // process all dwarf .o files as a batch
+               if ( someDwarf ) {
+                       // make mapping from readers with dwarf to ordinal
+                       std::map<class ObjectFile::Reader*, uint32_t>   readersWithDwarfOrdinals;
+                       uint32_t readerOrdinal = 1;
+                       for (std::vector<class ObjectFile::Reader*>::iterator it=fReadersThatHaveSuppliedAtoms.begin();
+                                       it != fReadersThatHaveSuppliedAtoms.end();
+                                       it++) {
+                               ObjectFile::Reader* reader = *it;
+                               if ( (reader != NULL) && (reader->getDebugInfoKind() == ObjectFile::Reader::kDebugInfoDwarf) ) {
+                                       readersWithDwarfOrdinals[reader] = readerOrdinal++;
+                               }
+                       }
+
+                       // make a vector of atoms
+                       std::vector<class ObjectFile::Atom*> allAtomsByReader(fAllAtoms.begin(), fAllAtoms.end());
+                       // remove those not from a reader that has dwarf
+                       allAtomsByReader.erase(std::remove_if(allAtomsByReader.begin(), allAtomsByReader.end(),
+                                                               NoDebugNoteAtom(readersWithDwarfOrdinals)), allAtomsByReader.end());
+                       // sort by reader then atom ordinal
+                       std::sort(allAtomsByReader.begin(), allAtomsByReader.end(), ReadersWithDwarfSorter(readersWithDwarfOrdinals, atomOrdinals));
+                       // add debug notes for each atom
+                       this->synthesizeDebugNotes(allAtomsByReader);
+               }
+
+               // process all stabs .o files one by one
+               if ( someStabs ) {
+                       // get stabs from each reader, in command line order
+                       for (std::vector<class ObjectFile::Reader*>::iterator it=fReadersThatHaveSuppliedAtoms.begin();
+                                       it != fReadersThatHaveSuppliedAtoms.end();
+                                       it++) {
+                               ObjectFile::Reader* reader = *it;
+                               if ( reader != NULL ) {
+                                       switch ( reader->getDebugInfoKind() ) {
+                                               case ObjectFile::Reader::kDebugInfoDwarf:
+                                               case ObjectFile::Reader::kDebugInfoNone:
+                                                       // do nothing
+                                                       break;
+                                               case ObjectFile::Reader::kDebugInfoStabs:
+                                               case ObjectFile::Reader::kDebugInfoStabsUUID:
+                                                       collectStabs(reader, atomOrdinals);
+                                                       break;
+                                               default:
+                                                       throw "Unhandled type of debug information";
+                                       }
+                               }
+                       }
+                       // remove stabs associated with atoms that won't be in output
+                       std::set<class ObjectFile::Atom*>       allAtomsSet;
+                       allAtomsSet.insert(fAllAtoms.begin(), fAllAtoms.end());
+                       fStabs.erase(std::remove_if(fStabs.begin(), fStabs.end(), NotInSet(allAtomsSet)), fStabs.end());
+               }
+       }
+}
+
+void Linker::writeOutput()
+{
+       if ( fOptions.forceCpuSubtypeAll() )
+               fCurrentCpuConstraint = ObjectFile::Reader::kCpuAny;
+               
+       fStartWriteTime = mach_absolute_time();
+       // tell writer about each segment's atoms
+       fOutputFileSize = fOutputFile->write(fAllAtoms, fStabs, this->entryPoint(), this->dyldHelper(),
+                                                                                       fCreateUUID, fCanScatter, 
+                                                                                       fCurrentCpuConstraint, fBiggerThanTwoGigOutput);
+}
 
 ObjectFile::Reader* Linker::createReader(const Options::FileInfo& info)
 {
@@ -814,122 +2703,206 @@ ObjectFile::Reader* Linker::createReader(const Options::FileInfo& info)
                throwf("can't open file, errno=%d", errno);
        if ( info.fileLen < 20 )
                throw "file too small";
-               
-       char* p = (char*)::mmap(NULL, info.fileLen, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0);
-       if ( p == (char*)(-1) )
+
+       uint8_t* p = (uint8_t*)::mmap(NULL, info.fileLen, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0);
+       if ( p == (uint8_t*)(-1) )
                throwf("can't map file, errno=%d", errno);
-       ::close(fd);
-       
+
        // if fat file, skip to architecture we want
-       const mach_header* mh = (mach_header*)p;
-       if ( mh->magic == OSSwapBigToHostInt32(FAT_MAGIC) ) {
+       const fat_header* fh = (fat_header*)p;
+       if ( fh->magic == OSSwapBigToHostInt32(FAT_MAGIC) ) {
                // Fat header is always big-endian
-               const struct fat_header* fh = (struct fat_header*)p;
                const struct fat_arch* archs = (struct fat_arch*)(p + sizeof(struct fat_header));
                for (unsigned long i=0; i < OSSwapBigToHostInt32(fh->nfat_arch); ++i) {
-                       if ( OSSwapBigToHostInt32(archs[i].cputype) == (uint32_t)fOptions.architecture() ) {
-                               mh = (struct mach_header*)((char*)p + OSSwapBigToHostInt32(archs[i].offset));
+                       if ( OSSwapBigToHostInt32(archs[i].cputype) == (uint32_t)fArchitecture ) {
+                               uint32_t fileOffset = OSSwapBigToHostInt32(archs[i].offset);
                                len = OSSwapBigToHostInt32(archs[i].size);
+                               // if requested architecture is page aligned within fat file, then remap just that portion of file
+                               if ( (fileOffset & 0x00000FFF) == 0 ) {
+                                       // unmap whole file
+                                       munmap((caddr_t)p, info.fileLen);
+                                       // re-map just part we need
+                                       p = (uint8_t*)::mmap(NULL, len, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, fileOffset);
+                                       if ( p == (uint8_t*)(-1) )
+                                               throwf("can't re-map file, errno=%d", errno);
+                               }
+                               else {
+                                       p = &p[fileOffset];
+                               }
                                break;
                        }
                }
        }
-       
-       if ( mh->magic == OSSwapBigToHostInt32(FAT_MAGIC) ) {
-               const char* archName = "unknown";
-               switch (fOptions.architecture()) {
-                       case CPU_TYPE_POWERPC:
-                               archName = "ppc";
-                               break;
-                       case CPU_TYPE_POWERPC64:
-                               archName = "ppc64";
-                               break;
-                       case CPU_TYPE_I386:
-                               archName = "i386";
-                               break;
-               }
-               throwf("missing required architecture %s in fat file", archName);
+       ::close(fd);
+
+       switch (fArchitecture) {
+               case CPU_TYPE_POWERPC:
+                       if ( mach_o::relocatable::Reader<ppc>::validFile(p) )
+                               return this->addObject(new mach_o::relocatable::Reader<ppc>::Reader(p, info.path, info.modTime, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       else if ( mach_o::dylib::Reader<ppc>::validFile(p, info.options.fBundleLoader) )
+                               return this->addDylib(new mach_o::dylib::Reader<ppc>::Reader(p, len, info.path, info.options.fBundleLoader, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       else if ( mach_o::archive::Reader<ppc>::validFile(p, len) )
+                               return this->addArchive(new mach_o::archive::Reader<ppc>::Reader(p, len, info.path, info.modTime, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       break;
+               case CPU_TYPE_POWERPC64:
+                       if ( mach_o::relocatable::Reader<ppc64>::validFile(p) )
+                               return this->addObject(new mach_o::relocatable::Reader<ppc64>::Reader(p, info.path, info.modTime, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       else if ( mach_o::dylib::Reader<ppc64>::validFile(p, info.options.fBundleLoader) )
+                               return this->addDylib(new mach_o::dylib::Reader<ppc64>::Reader(p, len, info.path, info.options.fBundleLoader, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       else if ( mach_o::archive::Reader<ppc64>::validFile(p, len) )
+                               return this->addArchive(new mach_o::archive::Reader<ppc64>::Reader(p, len, info.path, info.modTime, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       break;
+               case CPU_TYPE_I386:
+                       if ( mach_o::relocatable::Reader<x86>::validFile(p) )
+                               return this->addObject(new mach_o::relocatable::Reader<x86>::Reader(p, info.path, info.modTime, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       else if ( mach_o::dylib::Reader<x86>::validFile(p, info.options.fBundleLoader) )
+                               return this->addDylib(new mach_o::dylib::Reader<x86>::Reader(p, len, info.path, info.options.fBundleLoader, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       else if ( mach_o::archive::Reader<x86>::validFile(p, len) )
+                               return this->addArchive(new mach_o::archive::Reader<x86>::Reader(p, len, info.path, info.modTime, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       break;
+               case CPU_TYPE_X86_64:
+                       if ( mach_o::relocatable::Reader<x86_64>::validFile(p) )
+                               return this->addObject(new mach_o::relocatable::Reader<x86_64>::Reader(p, info.path, info.modTime, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       else if ( mach_o::dylib::Reader<x86_64>::validFile(p, info.options.fBundleLoader) )
+                               return this->addDylib(new mach_o::dylib::Reader<x86_64>::Reader(p, len, info.path, info.options.fBundleLoader, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       else if ( mach_o::archive::Reader<x86_64>::validFile(p, len) )
+                               return this->addArchive(new mach_o::archive::Reader<x86_64>::Reader(p, len, info.path, info.modTime, fOptions.readerOptions(), fNextInputOrdinal), info, len);
+                       break;
        }
-       
-       // pull out cpu-type and file-type in endian-safe way
-       cpu_type_t cpuType = 0;
-       uint32_t fileType = 0;
-       if ( mh->magic == MH_MAGIC ) {
-               fileType = mh->filetype;
-               cpuType = mh->cputype;
-       }
-       else if ( mh->magic == OSSwapInt32(MH_MAGIC) ) {
-               fileType = OSSwapInt32(mh->filetype);
-               cpuType = OSSwapInt32(mh->cputype);
-       }
-       else if ( mh->magic == MH_MAGIC_64 ) {
-               fileType = ((mach_header_64*)mh)->filetype;
-               cpuType = ((mach_header_64*)mh)->cputype;
-       }
-       else if ( mh->magic == OSSwapInt32(MH_MAGIC_64) ) {
-               fileType = OSSwapInt32(((mach_header_64*)mh)->filetype);
-               cpuType = OSSwapInt32(((mach_header_64*)mh)->cputype);
-       }
-       else if ( strncmp((const char*)mh, "!<arch>\n", 8) == 0 ) {
-               // is static archive
-               switch ( fOptions.architecture() ) {
-                       case CPU_TYPE_POWERPC:
-                               return ppc::ObjectFileArchiveMachO::MakeReader((const uint8_t*)mh, len, info.path, fOptions.readerOptions());
-                       case CPU_TYPE_POWERPC64:
-                               return ppc64::ObjectFileArchiveMachO::MakeReader((const uint8_t*)mh, len, info.path, fOptions.readerOptions());
-                       case CPU_TYPE_I386:
-                               return i386::ObjectFileArchiveMachO::MakeReader((const uint8_t*)mh, len, info.path, fOptions.readerOptions());
-               }
-               throw "no matching archive reader";
+
+#if LLVM_SUPPORT
+       if ( LLVMReader::validFile(p, info.path, fArchitecture, fOptions) ) {
+               return this->addObject(LLVMReader::make(p, info.path, info.modTime, fOptions), info, len);
+       }
+#endif
+       // error handling
+       if ( ((fat_header*)p)->magic == OSSwapBigToHostInt32(FAT_MAGIC) ) {
+               throwf("missing required architecture %s in file", fArchitectureName);
        }
        else {
-               throw "unknown file type";      
+               throw "file is not of required architecture";
        }
-       
-       // bail out if cpu-type does not match requrired architecture
-       if ( fOptions.architecture() == cpuType ) {
-               // make appropriate reader object
-               if ( fileType == MH_OBJECT ) {
-                       switch ( cpuType ) {
-                               case CPU_TYPE_POWERPC:
-                                       return ppc::ObjectFileMachO::MakeReader((class ppc::macho_header*)mh, info.path, fOptions.readerOptions());
-                               case CPU_TYPE_POWERPC64:
-                                       return ppc64::ObjectFileMachO::MakeReader((class ppc64::macho_header*)mh, info.path, fOptions.readerOptions());
-                               case CPU_TYPE_I386:
-                                       return i386::ObjectFileMachO::MakeReader((class i386::macho_header*)mh, info.path, fOptions.readerOptions());
-                               default:
-                                       throw "wrong architecture in object file";
-                       }
-               }
-               else if ( (fileType == MH_DYLIB) || (fileType == MH_DYLIB_STUB) ) {
-                       ObjectFile::Reader* dylibReader = NULL;
-                       switch ( cpuType ) {
-                               case CPU_TYPE_POWERPC:
-                                       dylibReader = ppc::ObjectFileDylibMachO::MakeReader((class ppc::macho_header*)mh, info.path, fOptions.readerOptions());
-                                       break;
-                               case CPU_TYPE_POWERPC64:
-                                       dylibReader = ppc64::ObjectFileDylibMachO::MakeReader((class ppc64::macho_header*)mh, info.path, fOptions.readerOptions());
-                                       break;
-                               case CPU_TYPE_I386:
-                                       dylibReader = i386::ObjectFileDylibMachO::MakeReader((class i386::macho_header*)mh, info.path, fOptions.readerOptions());
-                                       break;
-                               default:
-                                       throw "wrong architecture in dylib";
-                       }
-                       this->addDylib(dylibReader, info);
-                       return dylibReader;
-               }
-               throw "unknown mach-o file type";
+}
+
+void Linker::logDylib(ObjectFile::Reader* reader, bool indirect)
+{
+       if ( fOptions.readerOptions().fTraceDylibs ) {
+               const char* fullPath = reader->getPath();
+               char realName[MAXPATHLEN];
+               if ( realpath(fullPath, realName) != NULL )
+                       fullPath = realName;
+               if ( indirect )
+                       logTraceInfo("[Logging for XBS] Used indirect dynamic library: %s\n", fullPath);
+               else
+                       logTraceInfo("[Logging for XBS] Used dynamic library: %s\n", fullPath);
+       }
+}
+
+
+
+ObjectFile::Reader* Linker::findDylib(const char* installPath, const char* fromPath)
+{
+       //fprintf(stderr, "findDylib(%s, %s)\n", installPath, fromPath);
+       InstallNameToReader::iterator pos = fDylibMap.find(installPath);
+       if ( pos != fDylibMap.end() ) {
+               return pos->second;
        }
        else {
-               throw "file does not contain requested architecture";
+               // allow -dylib_path option to override indirect library to use
+               for (std::vector<Options::DylibOverride>::iterator dit = fOptions.dylibOverrides().begin(); dit != fOptions.dylibOverrides().end(); ++dit) {
+                       if ( strcmp(dit->installName,installPath) == 0 ) {\
+                               try {
+                                       Options::FileInfo info = fOptions.findFile(dit->useInstead);
+                                       ObjectFile::Reader* reader = this->createReader(info);
+                                       fDylibMap[strdup(installPath)] = reader;
+                                       this->logDylib(reader, true);
+                                       return reader;
+                               }
+                               catch (const char* msg) {
+                                       fprintf(stderr, "ld: warning ignoring -dylib_file option, %s\n", msg);
+                               }
+                       }
+               }
+               char newPath[MAXPATHLEN];
+               // handle @loader_path
+               if ( strncmp(installPath, "@loader_path/", 13) == 0 ) {
+                       strcpy(newPath, fromPath);
+                       char* addPoint = strrchr(newPath,'/');
+                       if ( addPoint != NULL )
+                               strcpy(&addPoint[1], &installPath[13]);
+                       else
+                               strcpy(newPath, &installPath[13]);
+                       installPath = newPath;
+               }
+               // note: @executable_path case is handled inside findFileUsingPaths()
+               // search for dylib using -F and -L paths
+               Options::FileInfo info = fOptions.findFileUsingPaths(installPath);
+               try {
+                       ObjectFile::Reader* reader = this->createReader(info);
+                       fDylibMap[strdup(installPath)] = reader;
+                       this->logDylib(reader, true);
+                       return reader;
+               }
+               catch (const char* msg) {
+                       throwf("in %s, %s", info.path, msg);
+               }
        }
+}
 
+
+void Linker::processDylibs()
+{
+       fAllDirectDylibsLoaded = true;
+
+       // mark all dylibs initially specified as required and check if they can be used
+       for (InstallNameToReader::iterator it=fDylibMap.begin(); it != fDylibMap.end(); it++) {
+               it->second->setExplicitlyLinked();
+               this->checkDylibClientRestrictions(it->second);
+       }
+       
+       // keep processing dylibs until no more dylibs are added
+       unsigned long lastMapSize = 0;
+       while ( lastMapSize != fDylibMap.size() ) {
+               lastMapSize = fDylibMap.size();
+               // can't iterator fDylibMap while modifying it, so use temp buffer
+               std::vector<ObjectFile::Reader*> currentUnprocessedReaders;
+               for (InstallNameToReader::iterator it=fDylibMap.begin(); it != fDylibMap.end(); it++) {
+                       if ( fDylibsProcessed.count(it->second) == 0 )
+                               currentUnprocessedReaders.push_back(it->second);
+               }
+               for (std::vector<ObjectFile::Reader*>::iterator it=currentUnprocessedReaders.begin(); it != currentUnprocessedReaders.end(); it++) {
+                       fDylibsProcessed.insert(*it);
+                       (*it)->processIndirectLibraries(this);
+               }
+       }
+       
+       // go back over original dylibs and mark sub frameworks as re-exported
+       if ( fOptions.outputKind() == Options::kDynamicLibrary ) {
+               const char* myLeaf = strrchr(fOptions.installPath(), '/');
+               if ( myLeaf != NULL ) {
+                       for (std::vector<class ObjectFile::Reader*>::iterator it=fInputFiles.begin(); it != fInputFiles.end(); it++) {
+                               ObjectFile::Reader* reader = *it;
+                               const char* childParent = reader->parentUmbrella();
+                               if ( childParent != NULL ) {
+                                       if ( strcmp(childParent, &myLeaf[1]) == 0 ) {
+                                               // set re-export bit of info
+                                               std::map<ObjectFile::Reader*,DynamicLibraryOptions>::iterator pos = fDylibOptionsMap.find(reader);
+                                               if ( pos != fDylibOptionsMap.end() ) {
+                                                       pos->second.fReExport = true;
+                                               }
+                                       }
+                               }
+                       }
+               }
+       }
+       
 }
 
+       
 
 void Linker::createReaders()
 {
+       fStartCreateReadersTime = mach_absolute_time();
        std::vector<Options::FileInfo>& files = fOptions.getInputFiles();
        const int count = files.size();
        if ( count == 0 )
@@ -940,7 +2913,7 @@ void Linker::createReaders()
                // ignore /usr/lib/dyld on command line in crt.o build
                if ( strcmp(entry.path, "/usr/lib/dyld") != 0 ) {
                        try {
-                               this->addInputFile(this->createReader(entry));
+                               this->addInputFile(this->createReader(entry), entry);
                        }
                        catch (const char* msg) {
                                if ( strstr(msg, "architecture") != NULL ) {
@@ -948,7 +2921,7 @@ void Linker::createReaders()
                                                // ignore, because this is about an architecture not in use
                                        }
                                        else {
-                                               fprintf(stderr, "ld64 warning: in %s, %s\n", entry.path, msg);
+                                               fprintf(stderr, "ld: warning in %s, %s\n", entry.path, msg);
                                        }
                                }
                                else {
@@ -957,168 +2930,259 @@ void Linker::createReaders()
                        }
                }
        }
-       
-       // add first level of indirect dylibs
-       fDirectLibrariesComplete = true;
-       for (std::vector<ExecutableFile::DyLibUsed>::iterator it=fDynamicLibraries.begin(); it != fDynamicLibraries.end(); it++) {
-               this->addIndirectLibraries(it->reader);
-       }
-       
-       // indirect handling depends on namespace
-       switch ( fOptions.nameSpace() ) {
-               case Options::kFlatNameSpace:
-               case Options::kForceFlatNameSpace:
-                       // with flat namespace, blindly load all indirect libraries
-                       // the indirect list will grow as indirect libraries are loaded
-                       for (std::list<IndirectLibrary>::iterator it=fIndirectDynamicLibraries.begin(); it != fIndirectDynamicLibraries.end(); it++) {
-                               try {
-                                       it->reader = this->createReader(fOptions.findFile(it->path));
-                               }
-                               catch (const char* msg) {
-                                       fprintf(stderr, "ld64 warning: indirect library %s could not be loaded: %s\n", it->path, msg);
-                               }
-                       }
-                       break;
-                       
-               case Options::kTwoLevelNameSpace:
-                       // with two-level namespace we only want to use indirect libraries that are re-exported through a library that is used
-                       {
-                               bool indirectAdded = true;
-                               while ( indirectAdded ) {
-                                       indirectAdded = false;
-                                       // instantiate a reader for each indirect library and try to find parent that re-exports it
-                                       for (std::list<IndirectLibrary>::iterator it=fIndirectDynamicLibraries.begin(); it != fIndirectDynamicLibraries.end(); it++) {
-                                               if ( it->reader == NULL ) {
-                                                       try {
-                                                               it->reader = this->createReader(fOptions.findFile(it->path));
-                                                               indirectAdded = true;
-                                                       }
-                                                       catch (const char* msg) {
-                                                               fprintf(stderr, "ld64 warning: indirect library %s could not be loaded: %s\n", it->path, msg);
-                                                       }
-                                               }
-                                               // if an indirect library does not have an assigned parent, look for one
-                                               if ( (it->reader != NULL) && (it->reExportParent == NULL) ) {
-                                                       // ask each parent if they re-export this dylib
-                                                       for (std::set<ObjectFile::Reader*>::iterator pit=it->parents.begin(); pit != it->parents.end(); pit++) {
-                                                               if ( (*pit)->reExports(it->reader) ) {
-                                                                       it->reExportParent = *pit;
-                                                                       break;
-                                                               }
-                                                       }
-                                               }
-                                       }
-                               }
-                       }
-                       break;
-       }
-       
-       // add relevant indirect libraries to the end of fDynamicLibraries
-       for (std::list<IndirectLibrary>::iterator it=fIndirectDynamicLibraries.begin(); it != fIndirectDynamicLibraries.end(); it++) {
-               if ( (it->reExportParent != NULL) || (fOptions.nameSpace() != Options::kTwoLevelNameSpace) ) {
-                       ExecutableFile::DyLibUsed dylibInfo;
-                       dylibInfo.reader = it->reader;
-                       dylibInfo.options.fWeakImport = false;
-                       dylibInfo.options.fReExport = false;
-                       dylibInfo.options.fInstallPathOverride = NULL;
-                       dylibInfo.indirect = true;
-                       dylibInfo.directReader = it->reExportParent;
-                       fDynamicLibraries.push_back(dylibInfo);
-                       if ( fOptions.readerOptions().fTraceIndirectDylibs )
-                               printf("[Logging for Build & Integration] Used indirect dynamic library: %s\n", it->reader->getPath());
-               }
-       }
+
+       this->processDylibs();
 }
 
 
 
-void Linker::addDylib(ObjectFile::Reader* reader, const Options::FileInfo& info)
+ObjectFile::Reader* Linker::addArchive(ObjectFile::Reader* reader, const Options::FileInfo& info, uint64_t mappedLen)
 {
-       if ( fDirectLibrariesComplete ) {
-               this->addIndirectLibraries(reader);
-       }
-       else {
-               if ( fOptions.readerOptions().fTraceDylibs )
-                       printf("[Logging for Build & Integration] Used dynamic library: %s\n", reader->getPath());
-               ExecutableFile::DyLibUsed dylibInfo;
-               dylibInfo.reader = reader;
-               dylibInfo.options = info.options;
-               dylibInfo.indirect = false;
-               dylibInfo.directReader = NULL;
-               fDynamicLibraries.push_back(dylibInfo);
-       }
+       fNextInputOrdinal += mappedLen;
+       // remember which readers are archives because they are logged differently
+       fArchiveReaders.insert(reader);
+
+       // update stats
+       fTotalArchiveSize += mappedLen;
+       ++fTotalArchivesLoaded;
+       return reader;
+}
+
+ObjectFile::Reader* Linker::addObject(ObjectFile::Reader* reader, const Options::FileInfo& info, uint64_t mappedLen)
+{
+       fNextInputOrdinal += mappedLen;
+       // any .o files that don't have MH_SUBSECTIONS_VIA_SYMBOLS, that means a generated .o file can't
+       if ( (fOptions.outputKind() == Options::kObjectFile) && !reader->canScatterAtoms() )
+               fCanScatter = false;
+
+       // update stats
+       fTotalObjectSize += mappedLen;
+       ++fTotalObjectLoaded;
+       return reader;
 }
 
 
-void Linker::addIndirectLibraries(ObjectFile::Reader* reader)
+void Linker::checkDylibClientRestrictions(ObjectFile::Reader* reader)
 {
-       std::vector<const char*>* dependentLibs = reader->getDependentLibraryPaths();
-       if ( dependentLibs != NULL ) {
-               for (std::vector<const char*>::iterator it=dependentLibs->begin(); it != dependentLibs->end(); it++) {
-                       if ( this->haveDirectLibrary(*it) ) {
-                               // do nothing, direct library already exists
+       // Check for any restrictions on who can link with this dylib  
+       const char* readerParentName = reader->parentUmbrella() ;
+       std::vector<const char*>* clients = reader->getAllowableClients();
+       if ( (readerParentName != NULL) || (clients != NULL) ) {
+               // only dylibs that are in an umbrella or have a client list need verification
+               const char* installName = fOptions.installPath();
+               const char* installNameLastSlash = strrchr(installName, '/');
+               bool isParent = false;
+               bool isSibling = false;
+               bool isAllowableClient = false;
+               // There are three cases:
+               if ( (readerParentName != NULL) && (installNameLastSlash != NULL) ) {
+                       // case 1) The dylib has a parent umbrella, and we are creating the parent umbrella
+                       isParent = ( strcmp(&installNameLastSlash[1], readerParentName) == 0 );
+                       
+                       // hack to support umbrella variants that encode the variant name in the install name 
+                       // e.g. CoreServices_profile
+                       if ( !isParent ) {
+                               const char* underscore = strchr(&installNameLastSlash[1], '_');
+                               if ( underscore != NULL ) {
+                                       isParent = ( strncmp(&installNameLastSlash[1], readerParentName, underscore-installNameLastSlash-1) == 0 );
+                               }
+                       }
+                       
+                       // case 2) The dylib has a parent umbrella, and we are creating a sibling with the same parent
+                       isSibling = ( (fOptions.umbrellaName() != NULL) && (strcmp(fOptions.umbrellaName(), readerParentName) == 0) );
+               }
+
+               if ( !isParent && !isSibling && (clients != NULL) ) {
+                       // case 3) the dylib has a list of allowable clients, and we are creating one of them
+                       const char* clientName = fOptions.clientName();
+                       int clientNameLen = 0;
+                       if ( clientName != NULL ) {
+                               // use client name as specified on command line
+                               clientNameLen = strlen(clientName);
+                       }
+                       else {
+                               // infer client name from output path (e.g. xxx/libfoo_variant.A.dylib --> foo, Bar.framework/Bar_variant --> Bar)
+                               clientName = installName;
+                               clientNameLen = strlen(clientName);
+                               // starts after last slash
+                               if ( installNameLastSlash != NULL )
+                                       clientName = &installNameLastSlash[1];
+                               if ( strncmp(clientName, "lib", 3) == 0 )
+                                       clientName = &clientName[3];
+                               // up to first dot
+                               const char* firstDot = strchr(clientName, '.');
+                               if ( firstDot != NULL )
+                                       clientNameLen = firstDot - clientName;
+                               // up to first underscore
+                               const char* firstUnderscore = strchr(clientName, '_');
+                               if ( (firstUnderscore != NULL) && ((firstUnderscore - clientName) < clientNameLen) )
+                                       clientNameLen = firstUnderscore - clientName;
+                       }
+
+                       // Use clientName to check if this dylib is able to link against the allowable clients.
+                       for (std::vector<const char*>::iterator it = clients->begin(); it != clients->end(); it++) {
+                               if ( strncmp(*it, clientName, clientNameLen) == 0 )
+                                       isAllowableClient = true;
                        }
-                       else if ( this->haveIndirectLibrary(*it, reader) ) {
-                               // side effect of haveIndirectLibrary() added reader to parent list
+               }
+       
+               if ( !isParent && !isSibling && !isAllowableClient ) {
+                       if ( readerParentName != NULL ) {
+                               throwf("cannot link directly with %s.  Link against the umbrella framework '%s.framework' instead.", 
+                                       reader->getPath(), readerParentName);
                        }
                        else {
-                               // add to list of indirect libraries
-                               IndirectLibrary indirectLib;
-                               indirectLib.path = *it;
-                               indirectLib.fileLen = 0;
-                               indirectLib.reader = NULL;
-                               indirectLib.parents.insert(reader);
-                               indirectLib.reExportParent = NULL;
-                               fIndirectDynamicLibraries.push_back(indirectLib);
-                               //fprintf(stderr, "add indirect library: %s\n", *it);
+                               throwf("cannot link directly with %s", reader->getPath());
                        }
                }
        }
+
+
 }
 
-bool Linker::haveIndirectLibrary(const char* path, ObjectFile::Reader* parentReader)
+ObjectFile::Reader* Linker::addDylib(ObjectFile::Reader* reader, const Options::FileInfo& info, uint64_t mappedLen)
 {
-       for (std::list<IndirectLibrary>::iterator it=fIndirectDynamicLibraries.begin(); it != fIndirectDynamicLibraries.end(); it++) {
-               if ( strcmp(path, it->path) == 0 ) {
-                       it->parents.insert(parentReader);
-                       return true;
+       fNextInputOrdinal += mappedLen;
+       if ( (reader->getInstallPath() == NULL) && !info.options.fBundleLoader ) {
+               // this is a "blank" stub
+               // silently ignore it
+               return reader;
+       }
+       // add to map of loaded dylibs
+       const char* installPath = reader->getInstallPath();
+       if ( installPath != NULL ) {
+               InstallNameToReader::iterator pos = fDylibMap.find(installPath);
+               if ( pos == fDylibMap.end() ) {
+                       fDylibMap[strdup(installPath)] = reader;
                }
-               if ( it->reader != NULL ) {
-                       const char* installPath = it->reader->getInstallPath();
-                       if ( (installPath != NULL) && (strcmp(path, installPath) == 0) )
-                               return true;
+               else {
+                       InstallNameToReader::iterator pos2 = fDylibMap.find(reader->getPath());
+                       if ( pos2 == fDylibMap.end() ) 
+                               fDylibMap[strdup(reader->getPath())] = reader;
+                       else
+                               fprintf(stderr, "ld: warning, duplicate dylib %s\n", reader->getPath());
                }
        }
-       return false;
+       else if ( info.options.fBundleLoader )
+               fBundleLoaderReader = reader;
+
+       // log direct readers
+       if ( !fAllDirectDylibsLoaded ) 
+               this->logDylib(reader, false);
+
+       // update stats
+       ++fTotalDylibsLoaded;
+
+       return reader;
 }
 
-bool Linker::haveDirectLibrary(const char* path)
+
+void Linker::logTraceInfo (const char* format, ...)
 {
-       for (std::vector<ExecutableFile::DyLibUsed>::iterator it=fDynamicLibraries.begin(); it != fDynamicLibraries.end(); it++) {
-               if ( strcmp(path, it->reader->getPath()) == 0 )
-                       return true;
-               const char* installPath = it->reader->getInstallPath();
-               if ( (installPath != NULL) && (strcmp(path, installPath) == 0) )
-                       return true;
+       static int trace_file = -1;
+       char trace_buffer[MAXPATHLEN * 2];
+       char *buffer_ptr;
+       int length;
+       ssize_t amount_written;
+       const char *trace_file_path = fOptions.readerOptions().fTraceOutputFile;
+
+       if(trace_file == -1) {
+               if(trace_file_path != NULL) {
+                       trace_file = open(trace_file_path, O_WRONLY | O_APPEND | O_CREAT, 0666);
+                       if(trace_file == -1)
+                               throwf("Could not open or create trace file: %s\n", trace_file_path);
+               }
+               else {
+                       trace_file = fileno(stderr);
+               }
        }
-       return false;
-}
 
+    va_list ap;
+       va_start(ap, format);
+       length = vsnprintf(trace_buffer, sizeof(trace_buffer), format, ap);
+       va_end(ap);
+       buffer_ptr = trace_buffer;
+
+       while(length > 0) {
+               amount_written = write(trace_file, buffer_ptr, length);
+               if(amount_written == -1)
+                       /* Failure to write shouldn't fail the build. */
+                       return;
+               buffer_ptr += amount_written;
+               length -= amount_written;
+       }
+}
 
 
 
 void Linker::createWriter()
 {
+       fStartCreateWriterTime = mach_absolute_time();
+
+       // make a vector out of all required dylibs in fDylibMap
+       std::vector<ExecutableFile::DyLibUsed>  dynamicLibraries;
+       // need to preserve command line order 
+       for (std::vector<class ObjectFile::Reader*>::iterator it=fInputFiles.begin(); it != fInputFiles.end(); it++) {
+               ObjectFile::Reader* reader = *it;
+               for (InstallNameToReader::iterator mit=fDylibMap.begin(); mit != fDylibMap.end(); mit++) {
+                       if ( reader == mit->second ) {
+                               ExecutableFile::DyLibUsed dylibInfo;
+                               dylibInfo.reader = reader;
+                               dylibInfo.options = fDylibOptionsMap[reader];
+                               dynamicLibraries.push_back(dylibInfo);
+                               break;
+                       }
+               }
+       }
+       // then add any other dylibs
+       for (InstallNameToReader::iterator it=fDylibMap.begin(); it != fDylibMap.end(); it++) {
+               if ( it->second->implicitlyLinked()  ) {
+                       // if not already in dynamicLibraries
+                       bool alreadyInDynamicLibraries = false;
+                       for (std::vector<ExecutableFile::DyLibUsed>::iterator dit=dynamicLibraries.begin(); dit != dynamicLibraries.end(); dit++) {
+                               if ( dit->reader == it->second ) {
+                                       alreadyInDynamicLibraries = true;
+                                       break;
+                               }
+                       }
+                       if ( ! alreadyInDynamicLibraries ) {    
+                               ExecutableFile::DyLibUsed dylibInfo;
+                               dylibInfo.reader = it->second;
+                               std::map<ObjectFile::Reader*,DynamicLibraryOptions>::iterator pos = fDylibOptionsMap.find(it->second);
+                               if ( pos != fDylibOptionsMap.end() ) {
+                                       dylibInfo.options = pos->second;
+                               }
+                               else {
+                                       dylibInfo.options.fWeakImport = false;          // FIX ME
+                                       dylibInfo.options.fReExport = false;
+                                       dylibInfo.options.fBundleLoader = false;
+                               }
+                               dynamicLibraries.push_back(dylibInfo);
+                       }
+               }
+       }
+       if ( fBundleLoaderReader != NULL ) {
+               ExecutableFile::DyLibUsed dylibInfo;
+               dylibInfo.reader = fBundleLoaderReader;
+               dylibInfo.options.fWeakImport = false;          
+               dylibInfo.options.fReExport = false;
+               dylibInfo.options.fBundleLoader = true;
+               dynamicLibraries.push_back(dylibInfo);
+       }
+
        const char* path = fOptions.getOutputFilePath();
-       switch ( fOptions.architecture() ) {
+       switch ( fArchitecture ) {
                case CPU_TYPE_POWERPC:
-                       this->setOutputFile(ppc::ExecutableFileMachO::MakeWriter(path, fOptions, fDynamicLibraries));
+                       this->setOutputFile(new mach_o::executable::Writer<ppc>(path, fOptions, dynamicLibraries));
                        break;
                case CPU_TYPE_POWERPC64:
-                       this->setOutputFile(ppc64::ExecutableFileMachO::MakeWriter(path, fOptions, fDynamicLibraries));
+                       this->setOutputFile(new mach_o::executable::Writer<ppc64>(path, fOptions, dynamicLibraries));
                        break;
                case CPU_TYPE_I386:
-                       this->setOutputFile(i386::ExecutableFileMachO::MakeWriter(path, fOptions, fDynamicLibraries));
+                       this->setOutputFile(new mach_o::executable::Writer<x86>(path, fOptions, dynamicLibraries));
+                       break;
+               case CPU_TYPE_X86_64:
+                       this->setOutputFile(new mach_o::executable::Writer<x86_64>(path, fOptions, dynamicLibraries));
                        break;
                default:
                        throw "unknown architecture";
@@ -1141,132 +3205,261 @@ void Linker::SymbolTable::require(const char* name)
        }
 }
 
-bool Linker::SymbolTable::add(ObjectFile::Atom& atom)
+// convenience labels for 2-dimensional switch statement
+enum AllDefinitionCombinations {
+       kRegAndReg                              = (ObjectFile::Atom::kRegularDefinition << 3)   | ObjectFile::Atom::kRegularDefinition,
+       kRegAndWeak                             = (ObjectFile::Atom::kRegularDefinition << 3)   | ObjectFile::Atom::kWeakDefinition,
+       kRegAndTent                             = (ObjectFile::Atom::kRegularDefinition << 3)   | ObjectFile::Atom::kTentativeDefinition,
+       kRegAndExtern                   = (ObjectFile::Atom::kRegularDefinition << 3)   | ObjectFile::Atom::kExternalDefinition,
+       kRegAndExternWeak               = (ObjectFile::Atom::kRegularDefinition << 3)   | ObjectFile::Atom::kExternalWeakDefinition,
+       kRegAndAbsolute                 = (ObjectFile::Atom::kRegularDefinition << 3)   | ObjectFile::Atom::kAbsoluteSymbol,
+       kWeakAndReg                             = (ObjectFile::Atom::kWeakDefinition << 3)              | ObjectFile::Atom::kRegularDefinition,
+       kWeakAndWeak                    = (ObjectFile::Atom::kWeakDefinition << 3)              | ObjectFile::Atom::kWeakDefinition,
+       kWeakAndTent                    = (ObjectFile::Atom::kWeakDefinition << 3)              | ObjectFile::Atom::kTentativeDefinition,
+       kWeakAndExtern                  = (ObjectFile::Atom::kWeakDefinition << 3)              | ObjectFile::Atom::kExternalDefinition,
+       kWeakAndExternWeak              = (ObjectFile::Atom::kWeakDefinition << 3)              | ObjectFile::Atom::kExternalWeakDefinition,
+       kWeakAndAbsolute                = (ObjectFile::Atom::kWeakDefinition << 3)              | ObjectFile::Atom::kAbsoluteSymbol,
+       kTentAndReg                             = (ObjectFile::Atom::kTentativeDefinition << 3) | ObjectFile::Atom::kRegularDefinition,
+       kTentAndWeak                    = (ObjectFile::Atom::kTentativeDefinition << 3) | ObjectFile::Atom::kWeakDefinition,
+       kTentAndTent                    = (ObjectFile::Atom::kTentativeDefinition << 3) | ObjectFile::Atom::kTentativeDefinition,
+       kTentAndExtern                  = (ObjectFile::Atom::kTentativeDefinition << 3) | ObjectFile::Atom::kExternalDefinition,
+       kTentAndExternWeak              = (ObjectFile::Atom::kTentativeDefinition << 3) | ObjectFile::Atom::kExternalWeakDefinition,
+       kTentAndAbsolute                = (ObjectFile::Atom::kTentativeDefinition << 3) | ObjectFile::Atom::kAbsoluteSymbol,
+       kExternAndReg                   = (ObjectFile::Atom::kExternalDefinition << 3)  | ObjectFile::Atom::kRegularDefinition,
+       kExternAndWeak                  = (ObjectFile::Atom::kExternalDefinition << 3)  | ObjectFile::Atom::kWeakDefinition,
+       kExternAndTent                  = (ObjectFile::Atom::kExternalDefinition << 3)  | ObjectFile::Atom::kTentativeDefinition,
+       kExternAndExtern                = (ObjectFile::Atom::kExternalDefinition << 3)  | ObjectFile::Atom::kExternalDefinition,
+       kExternAndExternWeak    = (ObjectFile::Atom::kExternalDefinition << 3)  | ObjectFile::Atom::kExternalWeakDefinition,
+       kExternAndAbsolute              = (ObjectFile::Atom::kExternalDefinition << 3)  | ObjectFile::Atom::kAbsoluteSymbol,
+       kExternWeakAndReg               = (ObjectFile::Atom::kExternalWeakDefinition << 3) | ObjectFile::Atom::kRegularDefinition,
+       kExternWeakAndWeak              = (ObjectFile::Atom::kExternalWeakDefinition << 3) | ObjectFile::Atom::kWeakDefinition,
+       kExternWeakAndTent              = (ObjectFile::Atom::kExternalWeakDefinition << 3) | ObjectFile::Atom::kTentativeDefinition,
+       kExternWeakAndExtern    = (ObjectFile::Atom::kExternalWeakDefinition << 3) | ObjectFile::Atom::kExternalDefinition,
+       kExternWeakAndExternWeak= (ObjectFile::Atom::kExternalWeakDefinition << 3) | ObjectFile::Atom::kExternalWeakDefinition,
+       kExternWeakAndAbsolute  = (ObjectFile::Atom::kExternalWeakDefinition << 3) | ObjectFile::Atom::kAbsoluteSymbol,
+       kAbsoluteAndReg                 = (ObjectFile::Atom::kAbsoluteSymbol << 3)              | ObjectFile::Atom::kRegularDefinition,
+       kAbsoluteAndWeak                = (ObjectFile::Atom::kAbsoluteSymbol << 3)              | ObjectFile::Atom::kWeakDefinition,
+       kAbsoluteAndTent                = (ObjectFile::Atom::kAbsoluteSymbol << 3)              | ObjectFile::Atom::kTentativeDefinition,
+       kAbsoluteAndExtern              = (ObjectFile::Atom::kAbsoluteSymbol << 3)              | ObjectFile::Atom::kExternalDefinition,
+       kAbsoluteAndExternWeak  = (ObjectFile::Atom::kAbsoluteSymbol << 3)              | ObjectFile::Atom::kExternalWeakDefinition,
+       kAbsoluteAndAbsolute    = (ObjectFile::Atom::kAbsoluteSymbol << 3)              | ObjectFile::Atom::kAbsoluteSymbol
+};
+
+bool Linker::SymbolTable::add(ObjectFile::Atom& newAtom)
 {
-       const bool log = false;
-       const char* name = atom.getName();
-       //fprintf(stderr, "map.add(%p: %s => %p)\n", &fTable, name, &atom);
+       bool useNew = true;
+       const char* name = newAtom.getName();
+       //fprintf(stderr, "map.add(%s => %p from %s)\n", name, &newAtom, newAtom.getFile()->getPath());
        Mapper::iterator pos = fTable.find(name);
-       if ( pos != fTable.end() ) {
-               ObjectFile::Atom* existingAtom = pos->second;
-               if ( existingAtom != NULL ) {
-                       if ( existingAtom->isTentativeDefinition() ) {
-                               if ( atom.isTentativeDefinition() ) {
-                                       if ( atom.getSize() > existingAtom->getSize() ) {
-                                               // replace common-symbol atom with another larger common-symbol
-                                               if ( fOwner.fOptions.warnCommons() ) 
-                                                       fprintf(stderr, "ld64: replacing common symbol %s size %lld from %s with larger symbol size %lld from %s\n", 
-                                                                       existingAtom->getName(), existingAtom->getSize(), existingAtom->getFile()->getPath(), atom.getSize(), atom.getFile()->getPath());
-                                               fOwner.fDeadAtoms.insert(existingAtom);
-                                               fTable[name] = &atom;
-                                               return true;
-                                       }
-                                       else {
-                                               // keep existing common-symbol atom
-                                               if ( fOwner.fOptions.warnCommons() ) {
-                                                       if ( atom.getSize() == existingAtom->getSize() ) 
-                                                               fprintf(stderr, "ld64: ignoring common symbol %s from %s because already have common from %s with same size\n", 
-                                                                       atom.getName(), atom.getFile()->getPath(), existingAtom->getFile()->getPath());
-                                                       else
-                                                               fprintf(stderr, "ld64: ignoring common symbol %s size %lld from %s because already have larger symbol size %lld from %s\n", 
-                                                                       atom.getName(), atom.getSize(), atom.getFile()->getPath(), existingAtom->getSize(), existingAtom->getFile()->getPath());
-                                               }
-                                               fOwner.fDeadAtoms.insert(&atom);
-                                               return false;
-                                       }
+       ObjectFile::Atom* existingAtom = NULL;
+       if ( pos != fTable.end() )
+               existingAtom = pos->second;
+       if ( existingAtom != NULL ) {
+               // already have atom with same name in symbol table
+               switch ( (AllDefinitionCombinations)((existingAtom->getDefinitionKind() << 3) | newAtom.getDefinitionKind()) ) {
+                       case kRegAndReg:
+                               throwf("duplicate symbol %s in %s and %s\n", name, newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                       case kRegAndWeak:
+                               // ignore new weak atom, because we already have a non-weak one
+                               useNew = false;
+                               break;
+                       case kRegAndTent:
+                               // ignore new tentative atom, because we already have a regular one
+                               useNew = false;
+                               if ( newAtom.getSize() > existingAtom->getSize() ) {
+                                       fprintf(stderr, "ld: warning for symbol %s tentative definition of size %llu from %s is "
+                                                                       "is smaller than the real definition of size %llu from %s\n",
+                                                                       newAtom.getDisplayName(), newAtom.getSize(), newAtom.getFile()->getPath(),
+                                                                       existingAtom->getSize(), existingAtom->getFile()->getPath());
+                               }
+                               break;
+                       case kRegAndExtern:
+                               // ignore external atom, because we already have a one
+                               useNew = false;
+                               break;
+                       case kRegAndExternWeak:
+                               // ignore external atom, because we already have a one
+                               useNew = false;
+                               break;
+                       case kRegAndAbsolute:
+                               throwf("duplicate symbol %s in %s and %s\n", name, newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                               break;
+                       case kWeakAndReg:
+                               // replace existing weak atom with regular one
+                               break;
+                       case kWeakAndWeak:
+                               // have another weak atom, use whichever has largest alignment requirement
+                               // because codegen of some client may require alignment
+                               useNew = ( newAtom.getAlignment().trailingZeros() > existingAtom->getAlignment().trailingZeros() );
+                               break;
+                       case kWeakAndTent:
+                               // replace existing weak atom with tentative one ???
+                               break;
+                       case kWeakAndExtern:
+                               // keep weak atom, at runtime external one may override
+                               useNew = false;
+                               break;
+                       case kWeakAndExternWeak:
+                               // keep weak atom, at runtime external one may override
+                               useNew = false;
+                               break;
+                       case kWeakAndAbsolute:
+                               // replace existing weak atom with absolute one
+                               break;
+                       case kTentAndReg:
+                               // replace existing tentative atom with regular one
+                               if ( newAtom.getSize() < existingAtom->getSize() ) {
+                                       fprintf(stderr, "ld: warning for symbol %s tentative definition of size %llu from %s is "
+                                                                       "being replaced by a real definition of size %llu from %s\n",
+                                                                       newAtom.getDisplayName(), existingAtom->getSize(), existingAtom->getFile()->getPath(),
+                                                                       newAtom.getSize(), newAtom.getFile()->getPath());
                                }
+                               break;
+                       case kTentAndWeak:
+                               // replace existing tentative atom with weak one ???
+                               break;
+                       case kTentAndTent:
+                               // use largest
+                               if ( newAtom.getSize() < existingAtom->getSize() ) {
+                                       useNew = false;
+                               } 
                                else {
-                                       // have common symbol, now found true defintion
-                                       if ( atom.isImportProxy() ) {
-                                               // definition is in a dylib, so commons-mode decides how to handle
-                                               switch ( fOwner.fOptions.commonsMode() ) {
-                                                       case Options::kCommonsIgnoreDylibs:
-                                                               if ( fOwner.fOptions.warnCommons() ) 
-                                                                       fprintf(stderr, "ld64: using common symbol %s from %s and ignoring defintion from dylib %s\n", 
-                                                                                       existingAtom->getName(), existingAtom->getFile()->getPath(), atom.getFile()->getPath());
-                                                               fOwner.fDeadAtoms.insert(&atom);
-                                                               return false;
-                                                       case Options::kCommonsOverriddenByDylibs:
-                                                               if ( fOwner.fOptions.warnCommons() ) 
-                                                                       fprintf(stderr, "ld64: replacing common symbol %s from %s with true definition from %s\n", 
-                                                                                       existingAtom->getName(), existingAtom->getFile()->getPath(), atom.getFile()->getPath());
-                                                               fOwner.fDeadAtoms.insert(existingAtom);
-                                                               fTable[name] = &atom;
-                                                               return true;
-                                                       case Options::kCommonsConflictsDylibsError:
-                                                               throwf("common symbol %s from %s conflicts with defintion from dylib %s", 
-                                                                               existingAtom->getName(), existingAtom->getFile()->getPath(), atom.getFile()->getPath());
-                                               }
-                                       }
-                                       else {
-                                               // replace common-symbol atom with true definition from .o file
-                                               if ( fOwner.fOptions.warnCommons() ) {
-                                                       if ( atom.getSize() < existingAtom->getSize() ) 
-                                                               fprintf(stderr, "ld64: warning: replacing common symbol %s size %lld from %s with smaller true definition size %lld from %s\n", 
-                                                                               existingAtom->getName(), existingAtom->getSize(), existingAtom->getFile()->getPath(), atom.getSize(), atom.getFile()->getPath());
-                                                       else
-                                                               fprintf(stderr, "ld64: replacing common symbol %s from %s with true definition from %s\n", 
-                                                                               existingAtom->getName(), existingAtom->getFile()->getPath(), atom.getFile()->getPath());
-                                               }
-                                               fOwner.fDeadAtoms.insert(existingAtom);
-                                               fTable[name] = &atom;
-                                               return true;
-                                       }
+                                       if ( newAtom.getAlignment().trailingZeros() < existingAtom->getAlignment().trailingZeros() )
+                                               fprintf(stderr, "ld: warning alignment lost in merging tentative definition %s\n", newAtom.getDisplayName());
                                }
-                       }
-                       else if ( atom.isTentativeDefinition() ) {
-                               // keep existing true definition, ignore new tentative definition
-                               if ( fOwner.fOptions.warnCommons() ) {
-                                       if ( atom.getSize() > existingAtom->getSize() ) 
-                                               fprintf(stderr, "ld64: warning: ignoring common symbol %s size %lld from %s because already have definition from %s size %lld, even though definition is smaller\n", 
-                                                       atom.getName(), atom.getSize(), atom.getFile()->getPath(), existingAtom->getFile()->getPath(), existingAtom->getSize());
-                                       else
-                                               fprintf(stderr, "ld64: ignoring common symbol %s from %s because already have definition from %s\n", 
-                                                       atom.getName(), atom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                               break;
+                       case kTentAndExtern:
+                       case kTentAndExternWeak:
+                               // a tentative definition and a dylib definition, so commons-mode decides how to handle
+                               switch ( fOwner.fOptions.commonsMode() ) {
+                                       case Options::kCommonsIgnoreDylibs:
+                                               if ( fOwner.fOptions.warnCommons() )
+                                                       fprintf(stderr, "ld: using common symbol %s from %s and ignoring defintion from dylib %s\n",
+                                                                       existingAtom->getName(), existingAtom->getFile()->getPath(), newAtom.getFile()->getPath());
+                                               useNew = false;
+                                               break;
+                                       case Options::kCommonsOverriddenByDylibs:
+                                               if ( fOwner.fOptions.warnCommons() )
+                                                       fprintf(stderr, "ld: replacing common symbol %s from %s with true definition from dylib %s\n",
+                                                                       existingAtom->getName(), existingAtom->getFile()->getPath(), newAtom.getFile()->getPath());
+                                               break;
+                                       case Options::kCommonsConflictsDylibsError:
+                                               throwf("common symbol %s from %s conflicts with defintion from dylib %s",
+                                                               existingAtom->getName(), existingAtom->getFile()->getPath(), newAtom.getFile()->getPath());
                                }
-                               fOwner.fDeadAtoms.insert(&atom);
-                               return false;
-                       }
-                       else {
-                               // neither existing nor new atom are tentative definitions
-                               // if existing is weak, we may replace it
-                               if ( existingAtom->isWeakDefinition() ) {
-                                       if ( atom.isImportProxy() ) {
-                                               // keep weak definition even though one exists in a dylib, because coalescing means dylib's copy may not be used
-                                               if ( log ) fprintf(stderr, "keep weak atom even though also in a dylib: %s\n", atom.getName());
-                                               fOwner.fDeadAtoms.insert(&atom);
-                                               return false;
-                                       }
-                                       else if ( atom.isWeakDefinition() ) {
-                                               // have another weak atom, use existing, mark new as dead
-                                               if ( log ) fprintf(stderr, "already have weak atom: %s\n", atom.getName());
-                                               fOwner.fDeadAtoms.insert(&atom);
-                                               return false;
-                                       }
-                                       else {
-                                               // replace weak atom with non-weak atom
-                                               if ( log ) fprintf(stderr, "replacing weak atom %p from %s with %p from %s: %s\n", existingAtom, existingAtom->getFile()->getPath(), &atom, atom.getFile()->getPath(), atom.getName());
-                                               fOwner.fDeadAtoms.insert(existingAtom);
-                                               fTable[name] = &atom;
-                                               return true;
-                                       }
+                               break;
+                       case kTentAndAbsolute:
+                               // replace tentative with absolute (can't size check because absolutes have no size)
+                               break;
+                       case kExternAndReg:
+                               // replace external atom with regular one
+                               break;
+                       case kExternAndWeak:
+                               // replace external atom with weak one
+                               break;
+                       case kExternAndTent:
+                               // a tentative definition and a dylib definition, so commons-mode decides how to handle
+                               switch ( fOwner.fOptions.commonsMode() ) {
+                                       case Options::kCommonsIgnoreDylibs:
+                                               if ( fOwner.fOptions.warnCommons() )
+                                                       fprintf(stderr, "ld: using common symbol %s from %s and ignoring defintion from dylib %s\n",
+                                                                       newAtom.getName(), newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                                               break;
+                                       case Options::kCommonsOverriddenByDylibs:
+                                               if ( fOwner.fOptions.warnCommons() )
+                                                       fprintf(stderr, "ld: replacing defintion of %s from dylib %s with common symbol from %s\n",
+                                                                       newAtom.getName(), existingAtom->getFile()->getPath(), newAtom.getFile()->getPath());
+                                               useNew = false;
+                                               break;
+                                       case Options::kCommonsConflictsDylibsError:
+                                               throwf("common symbol %s from %s conflicts with defintion from dylib %s",
+                                                                       newAtom.getName(), newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
                                }
-                       }
-                       if ( atom.isWeakDefinition() ) {
+                               break;
+                       case kExternAndExtern:
+                               throwf("duplicate symbol %s in %s and %s\n", name, newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                       case kExternAndExternWeak:
+                               // keep strong dylib atom, ignore weak one
+                               useNew = false;
+                               break;
+                       case kExternAndAbsolute:
+                               // replace external atom with absolute one
+                               break;
+                       case kExternWeakAndReg:
+                               // replace existing weak external with regular
+                               break;
+                       case kExternWeakAndWeak:
+                               // replace existing weak external with weak (let dyld decide at runtime which to use)
+                               break;
+                       case kExternWeakAndTent:
+                               // a tentative definition and a dylib definition, so commons-mode decides how to handle
+                               switch ( fOwner.fOptions.commonsMode() ) {
+                                       case Options::kCommonsIgnoreDylibs:
+                                               if ( fOwner.fOptions.warnCommons() )
+                                                       fprintf(stderr, "ld: using common symbol %s from %s and ignoring defintion from dylib %s\n",
+                                                                       newAtom.getName(), newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                                               break;
+                                       case Options::kCommonsOverriddenByDylibs:
+                                               if ( fOwner.fOptions.warnCommons() )
+                                                       fprintf(stderr, "ld: replacing defintion of %s from dylib %s with common symbol from %s\n",
+                                                                       newAtom.getName(), existingAtom->getFile()->getPath(), newAtom.getFile()->getPath());
+                                               useNew = false;
+                                               break;
+                                       case Options::kCommonsConflictsDylibsError:
+                                               throwf("common symbol %s from %s conflicts with defintion from dylib %s",
+                                                                       newAtom.getName(), newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                               }
+                               break;
+                       case kExternWeakAndExtern:
+                               // replace existing weak external with external
+                               break;
+                       case kExternWeakAndExternWeak:
+                               // keep existing external weak
+                               useNew = false;
+                               break;
+                       case kExternWeakAndAbsolute:
+                               // replace existing weak external with absolute
+                               break;
+                       case kAbsoluteAndReg:
+                               throwf("duplicate symbol %s in %s and %s\n", name, newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                       case kAbsoluteAndWeak:
                                // ignore new weak atom, because we already have a non-weak one
-                               return false;
-                       }
-                       if ( atom.isCoalesableByName() && existingAtom->isCoalesableByName() ) {
-                               // both coalesable, so ignore duplicate
-                               return false;
-                       }
-                       fprintf(stderr, "duplicate symbol %s in %s and %s\n", name, atom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                               useNew = false;
+                               break;
+                       case kAbsoluteAndTent:
+                               // ignore new tentative atom, because we already have a regular one
+                               useNew = false;
+                               break;
+                       case kAbsoluteAndExtern:
+                               // ignore external atom, because we already have a one
+                               useNew = false;
+                               break;
+                       case kAbsoluteAndExternWeak:
+                               // ignore external atom, because we already have a one
+                               useNew = false;
+                               break;
+                       case kAbsoluteAndAbsolute:
+                               throwf("duplicate symbol %s in %s and %s\n", name, newAtom.getFile()->getPath(), existingAtom->getFile()->getPath());
+                               break;
                }
        }
-       fTable[name] = &atom;
-       return true;
+       if ( (existingAtom != NULL) && (newAtom.getScope() != existingAtom->getScope()) ) {
+               fprintf(stderr, "ld: warning %s has different visibility (%d) in %s and (%d) in %s\n", 
+                       newAtom.getDisplayName(), newAtom.getScope(), newAtom.getFile()->getPath(), existingAtom->getScope(), existingAtom->getFile()->getPath());
+       }
+       if ( useNew ) {
+               fTable[name] = &newAtom;
+               if ( existingAtom != NULL )
+                       fOwner.fDeadAtoms.insert(existingAtom);
+       }
+       else {
+               fOwner.fDeadAtoms.insert(&newAtom);
+       }
+       return useNew;
 }
 
+
+
 ObjectFile::Atom* Linker::SymbolTable::find(const char* name)
 {
        Mapper::iterator pos = fTable.find(name);
@@ -1280,7 +3473,7 @@ ObjectFile::Atom* Linker::SymbolTable::find(const char* name)
 void Linker::SymbolTable::getNeededNames(bool andWeakDefintions, std::vector<const char*>& undefines)
 {
        for (Mapper::iterator it=fTable.begin(); it != fTable.end(); it++) {
-               if ( (it->second == NULL) || (andWeakDefintions && it->second->isWeakDefinition()) ) {
+               if ( (it->second == NULL) || (andWeakDefintions && (it->second->getDefinitionKind()==ObjectFile::Atom::kWeakDefinition)) ) {
                        undefines.push_back(it->first);
                }
        }
@@ -1289,45 +3482,88 @@ void Linker::SymbolTable::getNeededNames(bool andWeakDefintions, std::vector<con
 
 
 
-bool Linker::AtomSorter::operator()(ObjectFile::Atom* left, ObjectFile::Atom* right)
+bool Linker::AtomSorter::operator()(const ObjectFile::Atom* left, const ObjectFile::Atom* right)
 {
+       if ( left == right )
+               return false;
+
        // first sort by section order (which is already sorted by segment)
        unsigned int leftSectionIndex  =  left->getSection()->getIndex();
        unsigned int rightSectionIndex = right->getSection()->getIndex();
        if ( leftSectionIndex != rightSectionIndex)
                return (leftSectionIndex < rightSectionIndex);
-               
-       // with a section, sort by original atom order (.o file order and atom order in .o files)
-       return left->getSortOrder() < right->getSortOrder();
+
+       // if a -order_file is specified, then sorting is altered to sort those symbols first
+       if ( fOverriddenOrdinalMap != NULL ) {
+               std::map<const ObjectFile::Atom*, uint32_t>::iterator leftPos  = fOverriddenOrdinalMap->find(left);
+               std::map<const ObjectFile::Atom*, uint32_t>::iterator rightPos = fOverriddenOrdinalMap->find(right);
+               std::map<const ObjectFile::Atom*, uint32_t>::iterator end = fOverriddenOrdinalMap->end();
+               if ( leftPos != end ) {
+                       if ( rightPos != end ) {
+                               // both left and right are overridden, so compare overridden ordinals
+                               return leftPos->second < rightPos->second;
+                       }
+                       else {
+                               // left is overridden and right is not, so left < right
+                               return true;
+                       }
+               }
+               else {
+                       if ( rightPos != end ) {
+                               // right is overridden and left is not, so right < left
+                               return false;
+                       }
+                       else {
+                               // neither are overridden, do default sort
+                               // fall into default sorting below
+                       }
+               }
+       }
+       
+       // the __common section can have real or tentative definitions
+       // we want the real ones to sort before tentative ones
+       bool leftIsTent  =  (left->getDefinitionKind() == ObjectFile::Atom::kTentativeDefinition);
+       bool rightIsTent =  (right->getDefinitionKind() == ObjectFile::Atom::kTentativeDefinition);
+       if ( leftIsTent != rightIsTent )
+               return rightIsTent; 
+       
+       // lastly sort by atom ordinal.  this is already sorted by .o order
+       return left->getOrdinal() < right->getOrdinal();
 }
 
 
 int main(int argc, const char* argv[])
 {
+       const char* archName = NULL;
+       bool showArch = false;
+       bool archInferred = false;
        try {
                // create linker object given command line arguments
                Linker ld(argc, argv);
-               
+
+               // save error message prefix
+               archName = ld.architectureName();
+               archInferred = ld.isInferredArchitecture();
+               showArch = ld.showArchitectureInErrors();
+
                // open all input files
                ld.createReaders();
-               
+
                // open output file
                ld.createWriter();
-               
+
                // do linking
                ld.link();
        }
        catch (const char* msg) {
-               fprintf(stderr, "ld64 failed: %s\n", msg);
+               if ( archInferred )
+                       fprintf(stderr, "ld: %s for inferred architecture %s\n", msg, archName);
+               else if ( showArch )
+                       fprintf(stderr, "ld: %s for architecture %s\n", msg, archName);
+               else
+                       fprintf(stderr, "ld: %s\n", msg);
                return 1;
        }
-       
+
        return 0;
 }
-
-
-
-
-
-
-