[apple/dyld.git] / src / ImageLoaderMachO.cpp

/* -*- mode: C++; c-basic-offset: 4; tab-width: 4 -*-
 *
 * Copyright (c) 2004-2005 Apple Computer, 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,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * 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 <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h> 
#include <sys/mman.h>
#include <mach/shared_memory_server.h>
#include <mach/mach.h>
#include <mach/thread_status.h>
#include <mach-o/loader.h> 
#include <mach-o/reloc.h> 
#include <mach-o/nlist.h> 
#include <sys/sysctl.h>
#if __ppc__ || __ppc64__
        #include <mach-o/ppc/reloc.h>
#endif

#include "ImageLoaderMachO.h"
#include "mach-o/dyld_gdb.h"

// no header for this yet, rdar://problem/3850825
extern "C" void sys_icache_invalidate(void *, size_t);

// optimize strcmp for ppc
#if __ppc__
        #include <ppc_intrinsics.h>
#else
        #define astrcmp(a,b) strcmp(a,b)
#endif

// relocation_info.r_length field has value 3 for 64-bit executables and value 2 for 32-bit executables
#if __LP64__
        #define RELOC_SIZE 3
        #define LC_SEGMENT_COMMAND              LC_SEGMENT_64
        #define LC_ROUTINES_COMMAND             LC_ROUTINES_64
        struct macho_header                             : public mach_header_64  {};
        struct macho_segment_command    : public segment_command_64  {};
        struct macho_section                    : public section_64  {};        
        struct macho_nlist                              : public nlist_64  {};  
        struct macho_routines_command   : public routines_command_64  {};       
#else
        #define RELOC_SIZE 2
        #define LC_SEGMENT_COMMAND              LC_SEGMENT
        #define LC_ROUTINES_COMMAND             LC_ROUTINES
        struct macho_header                             : public mach_header  {};
        struct macho_segment_command    : public segment_command {};
        struct macho_section                    : public section  {};   
        struct macho_nlist                              : public nlist  {};     
        struct macho_routines_command   : public routines_command  {};  
#endif


uint32_t ImageLoaderMachO::fgHintedBinaryTreeSearchs = 0;
uint32_t ImageLoaderMachO::fgUnhintedBinaryTreeSearchs = 0;


//#define LINKEDIT_USAGE_DEBUG 1

#if LINKEDIT_USAGE_DEBUG
        #include <set>
        static std::set<uintptr_t> sLinkEditPageBuckets;

        namespace dyld {
                extern ImageLoader*     findImageContainingAddress(const void* addr);
        };

        static void noteAccessedLinkEditAddress(const void* addr)
        {
                uintptr_t page = ((uintptr_t)addr) & (-4096);
                sLinkEditPageBuckets.insert(page);
                fprintf(stderr, "dyld: accessing page 0x%08lX in __LINKEDIT of %s\n", page, dyld::findImageContainingAddress(addr)->getPath());
        }
#endif

// only way to share initialization in C++
void ImageLoaderMachO::init()
{
        fMachOData              = NULL;
        fLinkEditBase   = NULL;
        fSymbolTable    = NULL;
        fStrings                = NULL;
        fDynamicInfo    = NULL;
        fSlide                  = 0;
        fIsSplitSeg             = false;
        fHasSubLibraries= false;
        fHasSubUmbrella = false;
        fDashInit               = NULL;
        fModInitSection = NULL;
        fModTermSection = NULL;
        fDATAdyld               = NULL;
        fImageNotifySection     = NULL;
        fTwoLevelHints  = NULL;
        fDylibID                = NULL;
        fReExportThruFramework  = NULL;
        fTextSegmentWithFixups = NULL;
}

// create image by copying an in-memory mach-o file
ImageLoaderMachO::ImageLoaderMachO(const char* moduleName, const struct mach_header* mh, uint64_t len, const LinkContext& context)
 : ImageLoader(moduleName)
{
        // clean slate
        this->init();

        // temporary use this buffer until TEXT is mapped in
        fMachOData = (const uint8_t*)mh;

        // create segments
        this->instantiateSegments((const uint8_t*)mh);
        
        // map segments
        if ( mh->filetype != MH_EXECUTE )
                ImageLoader::mapSegments((const void*)mh, len, context);
        
        // get pointers to interesting things 
        this->parseLoadCmds();
}


// create image by mapping in a mach-o file
ImageLoaderMachO::ImageLoaderMachO(const char* path, int fd, const uint8_t firstPage[4096], uint64_t offsetInFat, 
                                                                        uint64_t lenInFat, const struct stat& info, const LinkContext& context)
 : ImageLoader(path, offsetInFat, info)
{       
        // clean slate
        this->init();

        // read load commands
        const unsigned int dataSize = sizeof(macho_header) + ((macho_header*)firstPage)->sizeofcmds;
        uint8_t buffer[dataSize];
        const uint8_t* fileData = firstPage;
        if ( dataSize > 4096 ) {
                // only read more if cmds take up more space than first page
                fileData = buffer;
                memcpy(buffer, firstPage, 4096);
                pread(fd, &buffer[4096], dataSize-4096, offsetInFat+4096);
        }
        
        // temporary use this buffer until TEXT is mapped in
        fMachOData = fileData;
        
        // the meaning of many fields changes in split seg mach-o files
        fIsSplitSeg = ((((macho_header*)fileData)->flags & MH_SPLIT_SEGS) != 0) && (((macho_header*)fileData)->filetype == MH_DYLIB);   
        
        // create segments
        this->instantiateSegments(fileData);
        
        // map segments, except for main executable which is already mapped in by kernel
        if ( ((macho_header*)fileData)->filetype != MH_EXECUTE )
                this->mapSegments(fd, offsetInFat, lenInFat, info.st_size, context);
                        
        // get pointers to interesting things 
        this->parseLoadCmds();
}




void ImageLoaderMachO::instantiateSegments(const uint8_t* fileData)
{
        const uint32_t cmd_count = ((macho_header*)fileData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fileData[sizeof(macho_header)];

        // construct Segment object for each LC_SEGMENT cmd and add to list
        const struct load_command* cmd = cmds;
        for (unsigned long i = 0; i < cmd_count; ++i) {
                if ( cmd->cmd == LC_SEGMENT_COMMAND ) {
                        fSegments.push_back(new SegmentMachO((struct macho_segment_command*)cmd, this, fileData));
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
}



bool ImageLoaderMachO::segmentsMustSlideTogether() const 
{
        return true;
}

bool ImageLoaderMachO::segmentsCanSlide() const 
{
        const macho_header* mh = (macho_header*)fMachOData;
        return ( (mh->filetype == MH_DYLIB) || (mh->filetype == MH_BUNDLE) );
}

bool ImageLoaderMachO::isBundle() const 
{
        const macho_header* mh = (macho_header*)fMachOData;
        return ( mh->filetype == MH_BUNDLE );
}

bool ImageLoaderMachO::isDylib() const 
{
        const macho_header* mh = (macho_header*)fMachOData;
        return ( mh->filetype == MH_DYLIB );
}

bool ImageLoaderMachO::forceFlat() const 
{
        const macho_header* mh = (macho_header*)fMachOData;
        return ( (mh->flags & MH_FORCE_FLAT) != 0 );
}

bool ImageLoaderMachO::usesTwoLevelNameSpace() const
{
        const macho_header* mh = (macho_header*)fMachOData;
        return ( (mh->flags & MH_TWOLEVEL) != 0 );
}

bool ImageLoaderMachO::isPrebindable() const 
{
        const macho_header* mh = (macho_header*)fMachOData;
        return ( (mh->flags & MH_PREBOUND) != 0 );
}

bool ImageLoaderMachO::hasCoalescedExports() const 
{
        const macho_header* mh = (macho_header*)fMachOData;
        return ( (mh->flags & MH_WEAK_DEFINES) != 0 );
}

bool ImageLoaderMachO::needsCoalescing() const 
{
        const macho_header* mh = (macho_header*)fMachOData;
        return ( (mh->flags & MH_BINDS_TO_WEAK) != 0 );
}

#if !__LP64__   // split segs not supported for 64-bits

#if 1 // hack until kernel headers and glue are in system
struct _shared_region_mapping_np {
    mach_vm_address_t   address;
    mach_vm_size_t      size;
    mach_vm_offset_t    file_offset;
        vm_prot_t               max_prot;   /* read/write/execute/COW/ZF */
        vm_prot_t               init_prot;  /* read/write/execute/COW/ZF */
};
struct _shared_region_range_np {
    mach_vm_address_t   address;
    mach_vm_size_t      size;
};
                
// Called by dyld.  
// Requests the kernel to map a number of regions from the fd into the
// shared sections address range (0x90000000-0xAFFFFFFF).
// If shared_region_make_private_np() has not been called by this process, 
// the file mapped in is seen in the address space of all processes that
// participate in using the shared region. 
// If shared_region_make_private_np() _has_ been called by this process, 
// the file mapped in is only seen by this process.
// If the slide parameter is not NULL and then regions cannot be mapped
// as requested, the kernel will try to map the file in at a different
// address in the shared region and return the distance slid. 
// If the mapping requesting cannot be fulfilled, returns non-zero.
static int 
_shared_region_map_file_np(
        int fd,                                                 // file descriptor to map into shared region
        unsigned int regionCount,               // number of entres in array of regions
        const _shared_region_mapping_np regions[],      // the array of regions to map
        uint64_t* slide)                                        // the amount all regions were slid,  NULL means don't attempt to slide
{
        //fprintf(stderr, "%s(%i, %u, %8p, %8p)\n", __func__, fd, regionCount, regions, slide);
        //for ( unsigned int i=0; i < regionCount; ++i) {
        //      fprintf(stderr, "\taddress=0x%08llX, size=0x%08llX\n", regions[i].address, regions[i].size);
        //}
        int r = syscall(299, fd, regionCount, regions, slide);
//      if(0 != r)
//              fprintf(stderr, "%s(%i, %u, %8p, %8p) errno=%i (%s)\n", __func__, fd, regionCount, regions, slide, errno, strerror(errno));
    return r;
}
// Called by dyld if shared_region_map_file() fails.
// Requests the kernel to take this process out of using the shared region.
// The specified ranges are created as private copies from the shared region for this process.
static int 
_shared_region_make_private_np(
        unsigned int rangeCount,                                // number of entres in array of msrp_range
        const _shared_region_range_np ranges[]) // the array of shared regions to make private
{
        //fprintf(stderr, "%s(%u, %8p)\n", __func__, rangeCount, ranges);
        int r = syscall(300, rangeCount, ranges);
//      if(0 != r)
//              fprintf(stderr, "%s(%u, %8p) errno=%i (%s)\n", __func__, rangeCount, ranges, errno, strerror(errno));
    return r;
}
#define KERN_SHREG_PRIVATIZABLE 54
#endif // hack until kernel headers and glue are in system

static uintptr_t sNextAltLoadAddress 
#if __ppc_
        = 0xC0000000;
#else
        = 0;
#endif


static
bool
hasSharedRegionMapFile(void)
{
        int     mib[CTL_MAXNAME];
        int     value = 0;
        size_t  size;

        mib[0] = CTL_KERN;
        mib[1] = KERN_SHREG_PRIVATIZABLE;
        size = sizeof (int);
        if (sysctl(mib, 2, &value, &size, NULL, 0) != 0) {
                value = 0;
        }

        return 0 != value;
}

int
ImageLoaderMachO::sharedRegionMapFilePrivateOutside(int fd,
                                                                                                        uint64_t offsetInFat,
                                                                                                        uint64_t lenInFat,
                                                                                                        uint64_t fileLen,
                                                                                                        const LinkContext& context)
{
        const unsigned int segmentCount = fSegments.size();
        const unsigned int extraZeroFillEntries = getExtraZeroFillEntriesCount();
        const unsigned int regionCount = segmentCount+extraZeroFillEntries;
        _shared_region_mapping_np regions[regionCount];
        initMappingTable(offsetInFat, regions);
        int r = -1;
                // find space somewhere to allocate split seg
                bool foundRoom = false;
                vm_size_t biggestDiff = 0;
                while ( ! foundRoom ) {
                        foundRoom = true;
                        for(unsigned int i=0; i < regionCount; ++i) {
                                vm_address_t addr = sNextAltLoadAddress + regions[i].address - regions[0].address;
                                vm_size_t size = regions[i].size ;
                                r = vm_allocate(mach_task_self(), &addr, size, false /*only this range*/);
                                if ( 0 != r ) {
                                        // no room here, deallocate what has succeeded so far
                                        for(unsigned int j=0; j < i; ++j) {
                                                vm_address_t addr = sNextAltLoadAddress + regions[j].address - regions[0].address;
                                                vm_size_t size = regions[j].size ;
                                                (void)vm_deallocate(mach_task_self(), addr, size);
                                        }
                                        sNextAltLoadAddress += 0x00100000;  // skip ahead 1MB and try again
                                        if ( (sNextAltLoadAddress & 0xF0000000) == 0x90000000 )
                                                throw "can't map split seg anywhere";
                                        foundRoom = false;
                                        break;
                                }
                                vm_size_t high = (regions[i].address + size - regions[0].address) & 0x0FFFFFFF;
                                if ( high > biggestDiff )
                                        biggestDiff = high;
                        }
                }
                
                // map in each region
                uintptr_t slide = sNextAltLoadAddress - regions[0].address;
                this->setSlide(slide);
                for(unsigned int i=0; i < regionCount; ++i) {
                        if ( (regions[i].init_prot & VM_PROT_ZF) != 0 ) {
                                // do nothing vm_allocate() zero-fills by default
                        }
                        else {
                                void* mmapAddress = (void*)(uintptr_t)(regions[i].address + slide);
                                size_t size = regions[i].size;
                                int protection = 0;
                                if ( regions[i].init_prot & VM_PROT_EXECUTE )
                                        protection   |= PROT_EXEC;
                                if ( regions[i].init_prot & VM_PROT_READ )
                                        protection   |= PROT_READ;
                                if ( regions[i].init_prot & VM_PROT_WRITE )
                                        protection   |= PROT_WRITE;
                                off_t offset = regions[i].file_offset;
                                //fprintf(stderr, "mmap(%p, 0x%08lX, block=0x%08X, %s\n", mmapAddress, size, biggestDiff, fPath);
                                mmapAddress = mmap(mmapAddress, size, protection, MAP_FILE | MAP_FIXED | MAP_PRIVATE, fd, offset);
                                if ( mmapAddress == ((void*)(-1)) )
                                        throw "mmap error";
                        }
                }
                // set so next maps right after this one
                sNextAltLoadAddress += biggestDiff; 
                sNextAltLoadAddress = (sNextAltLoadAddress + 4095) & (-4096);
                
                // logging
                if ( context.verboseMapping ) {
                        fprintf(stderr, "dyld: Mapping split-seg outside shared region, slid by 0x%08lX %s\n", this->fSlide, this->getPath());
                        for(unsigned int segIndex=0,entryIndex=0; segIndex < segmentCount; ++segIndex, ++entryIndex){
                                Segment* seg = fSegments[segIndex];
                                const _shared_region_mapping_np* entry = &regions[entryIndex];
                                if ( (entry->init_prot & VM_PROT_ZF) == 0 ) 
                                        fprintf(stderr, "%18s at 0x%08lX->0x%08lX\n",
                                                        seg->getName(), seg->getActualLoadAddress(), seg->getActualLoadAddress()+seg->getFileSize()-1);
                                if ( entryIndex < (regionCount-1) ) {
                                        const _shared_region_mapping_np* nextEntry = &regions[entryIndex+1];
                                        if ( (nextEntry->init_prot & VM_PROT_ZF) != 0 ) {
                                                uint64_t segOffset = nextEntry->address - entry->address;
                                                fprintf(stderr, "%18s at 0x%08lX->0x%08lX (zerofill)\n",
                                                                seg->getName(), (uintptr_t)(seg->getActualLoadAddress() + segOffset), (uintptr_t)(seg->getActualLoadAddress() + segOffset + nextEntry->size - 1));
                                                ++entryIndex;
                                        }
                                }
                        }
                }
                
                return r;
}


void ImageLoaderMachO::mapSegments(int fd, uint64_t offsetInFat, uint64_t lenInFat, uint64_t fileLen, const LinkContext& context)
{
        enum SharedRegionState
        {
                kSharedRegionStartState = 0,
                kSharedRegionLoadFileState,
                kSharedRegionMapFileState,
                kSharedRegionMapFilePrivateState,
                kSharedRegionMapFilePrivateOutsideState,
        };
        static SharedRegionState sSharedRegionState = kSharedRegionStartState;

        // non-split segment libraries handled by super class
        if ( !fIsSplitSeg )
                return ImageLoader::mapSegments(fd, offsetInFat, lenInFat, fileLen, context);
        
        if ( kSharedRegionStartState == sSharedRegionState ) {
                if ( hasSharedRegionMapFile() ) {
                        if ( (context.sharedRegionMode == kUsePrivateSharedRegion) || context.slideAndPackDylibs ) { 
                                sharedRegionMakePrivate(context);
                                sSharedRegionState = kSharedRegionMapFilePrivateState;
                        }
                        else if ( context.sharedRegionMode == kDontUseSharedRegion ) {
                                sSharedRegionState = kSharedRegionMapFilePrivateOutsideState;
                        }
                        else {
                                sSharedRegionState = kSharedRegionMapFileState;
                        }
                }
                else {
                        sSharedRegionState = kSharedRegionLoadFileState;
                }
        }
        
        if ( kSharedRegionLoadFileState == sSharedRegionState ) {
                if ( 0 != sharedRegionLoadFile(fd, offsetInFat, lenInFat, fileLen, context) ) {
                        sSharedRegionState = kSharedRegionMapFilePrivateOutsideState;
                }
        }
        else
        if ( kSharedRegionMapFileState == sSharedRegionState ) {
                if ( 0 != sharedRegionMapFile(fd, offsetInFat, lenInFat, fileLen, context) ) {
                        sharedRegionMakePrivate(context);
                        sSharedRegionState = kSharedRegionMapFilePrivateState;
                }
        }
        
        if ( kSharedRegionMapFilePrivateState == sSharedRegionState ) {
                if ( 0 != sharedRegionMapFilePrivate(fd, offsetInFat, lenInFat, fileLen, context) ) {
                        sSharedRegionState = kSharedRegionMapFilePrivateOutsideState;
                }
        }
        
        if ( kSharedRegionMapFilePrivateOutsideState == sSharedRegionState ) {
                if ( 0 != sharedRegionMapFilePrivateOutside(fd, offsetInFat, lenInFat, fileLen, context) ) {
                        throw "mapping error";
                }
        }
}

unsigned int
ImageLoaderMachO::getExtraZeroFillEntriesCount()
{
        // calculate mapping entries
        const unsigned int segmentCount = fSegments.size();
        unsigned int extraZeroFillEntries = 0;
        for(unsigned int i=0; i < segmentCount; ++i){
                Segment* seg = fSegments[i];
                if ( seg->hasTrailingZeroFill() )
                        ++extraZeroFillEntries;
        }
        
        return extraZeroFillEntries;
}

void
ImageLoaderMachO::initMappingTable(uint64_t offsetInFat,
                                                                   _shared_region_mapping_np *mappingTable)
{
        unsigned int segmentCount = fSegments.size();
        for(unsigned int segIndex=0,entryIndex=0; segIndex < segmentCount; ++segIndex, ++entryIndex){
                Segment* seg = fSegments[segIndex];
                _shared_region_mapping_np* entry = &mappingTable[entryIndex];
                entry->address                  = seg->getActualLoadAddress();
                entry->size                             = seg->getFileSize();
                entry->file_offset              = seg->getFileOffset() + offsetInFat;
                entry->init_prot                = VM_PROT_NONE;
                if ( !seg->unaccessible() ) {
                        if ( seg->executable() )
                                entry->init_prot   |= VM_PROT_EXECUTE;
                        if ( seg->readable() )
                                entry->init_prot   |= VM_PROT_READ;
                        if ( seg->writeable() )
                                entry->init_prot   |= VM_PROT_WRITE | VM_PROT_COW;
                }
                entry->max_prot                 = entry->init_prot;
                if ( seg->hasTrailingZeroFill() ) {
                        _shared_region_mapping_np* zfentry = &mappingTable[++entryIndex];
                        zfentry->address                = entry->address + seg->getFileSize();
                        zfentry->size                   = seg->getSize() - seg->getFileSize();
                        zfentry->file_offset    = 0;
                        zfentry->init_prot              = entry->init_prot | VM_PROT_COW | VM_PROT_ZF;
                        zfentry->max_prot               = zfentry->init_prot;
                }
        }
}
        
int
ImageLoaderMachO::sharedRegionMakePrivate(const LinkContext& context)
{
        if ( context.verboseMapping )
                fprintf(stderr, "dyld: making shared regions private\n");

        // shared mapping failed, so make private copy of shared region and try mapping private
        RegionsVector allRegions;
        context.getAllMappedRegions(allRegions);
        std::vector<_shared_region_range_np> splitSegRegions;
        const unsigned int allRegiontCount = allRegions.size();
        for(unsigned int i=0; i < allRegiontCount; ++i){
                MappedRegion region = allRegions[i];
                uint8_t highByte = region.address >> 28;
                if ( (highByte == 9) || (highByte == 0xA) ) {
                        _shared_region_range_np splitRegion;
                        splitRegion.address = region.address;
                        splitRegion.size = region.size;
                        splitSegRegions.push_back(splitRegion);
                }
        }
        int result = _shared_region_make_private_np(splitSegRegions.size(), &splitSegRegions[0]);
        // notify gdb or other lurkers that this process is no longer using the shared region
        dyld_all_image_infos.processDetachedFromSharedRegion = true;
        return result;
}

int
ImageLoaderMachO::sharedRegionMapFile(int fd,
                                         uint64_t offsetInFat,
                                         uint64_t lenInFat,
                                         uint64_t fileLen,
                                         const LinkContext& context)
{
        // build table of segments to map
        const unsigned int segmentCount = fSegments.size();
        const unsigned int extraZeroFillEntries = getExtraZeroFillEntriesCount();
        const unsigned int mappingTableCount = segmentCount+extraZeroFillEntries;
        _shared_region_mapping_np mappingTable[mappingTableCount];
        initMappingTable(offsetInFat, mappingTable);
//      uint64_t slide;
        uint64_t *slidep = NULL;

        // try to map it in shared
        int r = _shared_region_map_file_np(fd, mappingTableCount, mappingTable, slidep);
        if ( 0 == r ) {
                if(NULL != slidep && 0 != *slidep) {
                        // update with actual load addresses
                }
                if ( context.verboseMapping ) {
                        fprintf(stderr, "dyld: Mapping split-seg shared %s\n", this->getPath());
                        for(unsigned int segIndex=0,entryIndex=0; segIndex < segmentCount; ++segIndex, ++entryIndex){
                                Segment* seg = fSegments[segIndex];
                                const _shared_region_mapping_np* entry = &mappingTable[entryIndex];
                                if ( (entry->init_prot & VM_PROT_ZF) == 0 ) 
                                        fprintf(stderr, "%18s at 0x%08lX->0x%08lX\n",
                                                        seg->getName(), seg->getActualLoadAddress(), seg->getActualLoadAddress()+seg->getFileSize()-1);
                                if ( entryIndex < (mappingTableCount-1) ) {
                                        const _shared_region_mapping_np* nextEntry = &mappingTable[entryIndex+1];
                                        if ( (nextEntry->init_prot & VM_PROT_ZF) != 0 ) {
                                                uint64_t segOffset = nextEntry->address - entry->address;
                                                fprintf(stderr, "%18s at 0x%08lX->0x%08lX\n",
                                                                seg->getName(), (uintptr_t)(seg->getActualLoadAddress() + segOffset), (uintptr_t)(seg->getActualLoadAddress() + segOffset + nextEntry->size - 1));
                                                ++entryIndex;
                                        }
                                }
                        }
                }
        }
        return r;
}

int
ImageLoaderMachO::sharedRegionMapFilePrivate(int fd,
                                                                                         uint64_t offsetInFat,
                                                                                         uint64_t lenInFat,
                                                                                         uint64_t fileLen,
                                                                                         const LinkContext& context)
{
        const unsigned int segmentCount = fSegments.size();

        // adjust base address of segments to pack next to last dylib
        if ( context.slideAndPackDylibs ) {
                uintptr_t lowestReadOnly = (uintptr_t)(-1);
                uintptr_t lowestWritable = (uintptr_t)(-1);
                for(unsigned int segIndex=0; segIndex < segmentCount; ++segIndex){
                        Segment* seg = fSegments[segIndex];
                        uintptr_t segEnd = seg->getActualLoadAddress();
                        if ( seg->writeable() ) {
                                if ( segEnd < lowestWritable )
                                        lowestWritable = segEnd;
                        }
                        else {
                                if ( segEnd < lowestReadOnly )
                                        lowestReadOnly = segEnd;
                        }
                }
                uintptr_t baseAddress;
                if ( lowestWritable - 256*1024*1024 < lowestReadOnly )
                        baseAddress = lowestWritable - 256*1024*1024;
                else
                        baseAddress = lowestReadOnly;
                // record that we want dylb slid to fgNextSplitSegAddress
                this->setSlide(fgNextSplitSegAddress - baseAddress);
        }
        
        // build table of segments to map
        const unsigned int extraZeroFillEntries = getExtraZeroFillEntriesCount();
        const unsigned int mappingTableCount = segmentCount+extraZeroFillEntries;
        _shared_region_mapping_np mappingTable[mappingTableCount];
        initMappingTable(offsetInFat, mappingTable);
        uint64_t slide = 0;

        // try map it in privately (don't allow sliding if we pre-calculated the load address to pack dylibs)
        int r = _shared_region_map_file_np(fd, mappingTableCount, mappingTable, context.slideAndPackDylibs ? NULL : &slide);
        if ( 0 == r ) {
                if ( 0 != slide ) {
                        slide = (slide) & (-4096); // round down to page boundary
                        this->setSlide(slide);
                }
                if ( context.verboseMapping ) {
                        if ( slide == 0 )
                                fprintf(stderr, "dyld: Mapping split-seg un-shared %s\n", this->getPath());
                        else
                                fprintf(stderr, "dyld: Mapping split-seg un-shared slid by 0x%08llX %s\n", slide, this->getPath());
                        for(unsigned int segIndex=0,entryIndex=0; segIndex < segmentCount; ++segIndex, ++entryIndex){
                                Segment* seg = fSegments[segIndex];
                                const _shared_region_mapping_np* entry = &mappingTable[entryIndex];
                                if ( (entry->init_prot & VM_PROT_ZF) == 0 ) 
                                        fprintf(stderr, "%18s at 0x%08lX->0x%08lX\n",
                                                        seg->getName(), seg->getActualLoadAddress(), seg->getActualLoadAddress()+seg->getFileSize()-1);
                                if ( entryIndex < (mappingTableCount-1) ) {
                                        const _shared_region_mapping_np* nextEntry = &mappingTable[entryIndex+1];
                                        if ( (nextEntry->init_prot & VM_PROT_ZF) != 0 ) {
                                                uint64_t segOffset = nextEntry->address - entry->address;
                                                fprintf(stderr, "%18s at 0x%08lX->0x%08lX (zerofill)\n",
                                                                seg->getName(), (uintptr_t)(seg->getActualLoadAddress() + segOffset), (uintptr_t)(seg->getActualLoadAddress() + segOffset + nextEntry->size - 1));
                                                ++entryIndex;
                                        }
                                }
                        }
                }
                if ( context.slideAndPackDylibs ) {
                        // calculate where next split-seg dylib can load
                        uintptr_t largestReadOnly = 0;
                        uintptr_t largestWritable = 0;
                        for (unsigned int segIndex=0; segIndex < segmentCount; ++segIndex) {
                                Segment* seg = fSegments[segIndex];
                                uintptr_t segEnd = seg->getActualLoadAddress()+seg->getSize();
                                segEnd = (segEnd+4095) & (-4096); // page align
                                if ( seg->writeable() ) {
                                        if ( segEnd > largestWritable )
                                                largestWritable = segEnd;
                                }
                                else {
                                        if ( segEnd > largestReadOnly )
                                                largestReadOnly = segEnd;
                                }
                        }
                        if ( largestWritable - 256*1024*1024 > largestReadOnly )
                                fgNextSplitSegAddress = largestWritable - 256*1024*1024;
                        else
                                fgNextSplitSegAddress = largestReadOnly;
                }
        }
        if ( context.slideAndPackDylibs && (r != 0) )
                throw "can't rebase split-seg dylib";
        
        return r;
}


int
ImageLoaderMachO::sharedRegionLoadFile(int fd, uint64_t offsetInFat, uint64_t lenInFat, uint64_t fileLen, const LinkContext& context)
{
        
        // map in split segment file at random address, then tell kernel to share it
        void* loadAddress = 0;
        loadAddress = mmap(NULL, fileLen, PROT_READ, MAP_FILE, fd, 0);
        if ( loadAddress == ((void*)(-1)) )
                throw "mmap error";

        // calculate mapping entries
        const unsigned int segmentCount = fSegments.size();
        unsigned int extraZeroFillEntries = getExtraZeroFillEntriesCount();
        
        // build table of segments to map
        const unsigned int mappingTableCount = segmentCount+extraZeroFillEntries;
        const uintptr_t baseAddress = fSegments[0]->getPreferredLoadAddress();
        sf_mapping mappingTable[mappingTableCount];
        initMappingTable(offsetInFat, mappingTable, baseAddress);
        
        
        // use load_shared_file() to map all segments at once
        int flags = 0; // might need to set NEW_LOCAL_SHARED_REGIONS on first use
        static bool firstTime = true;
        if ( firstTime ) {
                // when NEW_LOCAL_SHARED_REGIONS bit is set, this process will get is own shared region
                // this is used by Xcode to prevent development libraries from polluting the global shared segment
                if ( context.sharedRegionMode == kUsePrivateSharedRegion )
                        flags |= NEW_LOCAL_SHARED_REGIONS;
                firstTime = false;
        }
        
        caddr_t base_address = (caddr_t)baseAddress;
        kern_return_t r;
        r = load_shared_file(   (char*)fPath,           // path of file to map shared
                                                        (char*)loadAddress, // beginning of local copy of sharable pages in file
                                                        fileLen,                        // end of shareable pages in file
                                                        &base_address,          // beginning of address range to map
                                                        mappingTableCount,  // number of entres in array of sf_mapping
                                                        mappingTable,           // the array of sf_mapping
                                                        &flags);                        // in/out flags
        if ( 0 != r ) {
                // try again but tell kernel it is ok to slide
                flags |= ALTERNATE_LOAD_SITE;
                r = load_shared_file((char*)fPath,(char*)loadAddress, fileLen, &base_address,   
                                                        mappingTableCount, mappingTable, &flags);
        }
        
        // unmap file from random address now that they are (hopefully) mapped into the shared region
        munmap(loadAddress, fileLen);

        if ( 0 == r ) {
                if ( base_address != (caddr_t)baseAddress )
                        this->setSlide((uintptr_t)base_address - baseAddress);
                if ( context.verboseMapping ) {
                        if ( base_address != (caddr_t)baseAddress )
                                fprintf(stderr, "dyld: Mapping split-seg load_shared_alt_region %s\n", this->getPath());
                        else
                                fprintf(stderr, "dyld: Mapping split-seg load_shared %s\n", this->getPath());
                        for(unsigned int segIndex=0,entryIndex=0; segIndex < segmentCount; ++segIndex, ++entryIndex){
                                Segment* seg = fSegments[segIndex];
                                const sf_mapping* entry = &mappingTable[entryIndex];
                                if ( (entry->protection & VM_PROT_ZF) == 0 )
                                        fprintf(stderr, "%18s at 0x%08lX->0x%08lX\n",
                                                        seg->getName(), seg->getActualLoadAddress(), seg->getActualLoadAddress()+seg->getFileSize()-1);
                                if ( entryIndex < (mappingTableCount-1) ) {
                                        const sf_mapping* nextEntry = &mappingTable[entryIndex+1];
                                        if ( (nextEntry->protection & VM_PROT_ZF) != 0 ) {
                                                fprintf(stderr, "%18s at 0x%08lX->0x%08lX\n",
                                                        seg->getName(), (uintptr_t)(nextEntry->mapping_offset + base_address), (uintptr_t)(nextEntry->mapping_offset + base_address + nextEntry->size - 1));
                                                ++entryIndex;
                                        }
                                }
                        }
                }
        }
        return r;
}
void
ImageLoaderMachO::initMappingTable(uint64_t offsetInFat,
                                                                   sf_mapping *mappingTable,
                                                                   uintptr_t baseAddress)
{
        unsigned int segmentCount = fSegments.size();
        for(unsigned int segIndex=0,entryIndex=0; segIndex < segmentCount; ++segIndex, ++entryIndex){
                Segment* seg = fSegments[segIndex];
                sf_mapping* entry = &mappingTable[entryIndex];
                entry->mapping_offset   = seg->getPreferredLoadAddress() - baseAddress;
                entry->size                             = seg->getFileSize();
                entry->file_offset              = seg->getFileOffset() + offsetInFat;
                entry->protection               = VM_PROT_NONE;
                if ( !seg->unaccessible() ) {
                        if ( seg->executable() )
                                entry->protection   |= VM_PROT_EXECUTE;
                        if ( seg->readable() )
                                entry->protection   |= VM_PROT_READ;
                        if ( seg->writeable() )
                                entry->protection   |= VM_PROT_WRITE | VM_PROT_COW;
                }
                
                entry->cksum                    = 0;
                if ( seg->hasTrailingZeroFill() ) {
                        sf_mapping* zfentry = &mappingTable[++entryIndex];
                        zfentry->mapping_offset = entry->mapping_offset + seg->getFileSize();
                        zfentry->size                   = seg->getSize() - seg->getFileSize();
                        zfentry->file_offset    = 0;
                        zfentry->protection             = entry->protection | VM_PROT_COW | VM_PROT_ZF;
                        zfentry->cksum                  = 0;
                }
        }
}

#endif //  !__LP64__  split segs not supported for 64-bits


void ImageLoaderMachO::setSlide(intptr_t slide)
{
        fSlide = slide;
}

void ImageLoaderMachO::parseLoadCmds()
{
        // now that segments are mapped in, get real fMachOData, fLinkEditBase, and fSlide
        const unsigned int segmentCount = fSegments.size();
        for(unsigned int i=0; i < segmentCount; ++i){
                Segment* seg = fSegments[i];
                // set up pointer to __LINKEDIT segment
                if ( strcmp(seg->getName(),"__LINKEDIT") == 0 ) 
                        fLinkEditBase = (uint8_t*)(seg->getActualLoadAddress() - seg->getFileOffset());
                // __TEXT segment always starts at beginning of file and contains mach_header and load commands
                if ( strcmp(seg->getName(),"__TEXT") == 0 ) {
                        if ( seg->hasFixUps() )
                                fTextSegmentWithFixups = (SegmentMachO*)seg;
                }
                // some segment always starts at beginning of file and contains mach_header and load commands
                if ( (seg->getFileOffset() == 0) && (seg->getFileSize() != 0) ) {
                        fMachOData = (uint8_t*)(seg->getActualLoadAddress());
                }
        }

        // walk load commands (mapped in at start of __TEXT segment)
        const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        for (uint32_t i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_SYMTAB:
                                {
                                        const struct symtab_command* symtab = (struct symtab_command*)cmd;
                                        fStrings = (const char*)&fLinkEditBase[symtab->stroff];
                                        fSymbolTable = (struct macho_nlist*)(&fLinkEditBase[symtab->symoff]);
                                }
                                break;
                        case LC_DYSYMTAB:
                                fDynamicInfo = (struct dysymtab_command*)cmd;
                                break;
                        case LC_SUB_UMBRELLA:
                                fHasSubUmbrella = true;
                                break;
                        case LC_SUB_FRAMEWORK:
                                {
                                        const struct sub_framework_command* subf = (struct sub_framework_command*)cmd;
                                        fReExportThruFramework = (char*)cmd + subf->umbrella.offset;
                                }
                                break;
                        case LC_SUB_LIBRARY:
                                fHasSubLibraries = true;
                                break;
                        case LC_ROUTINES_COMMAND:
                                fDashInit = (struct macho_routines_command*)cmd;
                                break;
                        case LC_SEGMENT_COMMAND:
                                {
                                        const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
                                        const bool isDataSeg = (strcmp(seg->segname, "__DATA") == 0);
                                        const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
                                        const struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
                                        for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
                                                const uint8_t type = sect->flags & SECTION_TYPE;
                                                if ( type == S_MOD_INIT_FUNC_POINTERS )
                                                        fModInitSection = sect;
                                                else if ( type == S_MOD_TERM_FUNC_POINTERS )
                                                        fModTermSection = sect;
                                                else if ( isDataSeg && (strcmp(sect->sectname, "__dyld") == 0) )
                                                        fDATAdyld = sect;
                                                else if ( isDataSeg && (strcmp(sect->sectname, "__image_notify") == 0) )
                                                        fImageNotifySection = sect;
                                        }
                                }
                                break;
                        case LC_TWOLEVEL_HINTS:
                                fTwoLevelHints = (struct twolevel_hints_command*)cmd;
                                break;
                        case LC_ID_DYLIB:
                                {
                                        fDylibID = (struct dylib_command*)cmd;
                                }
                                break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
}




const char* ImageLoaderMachO::getInstallPath() const
{
        if ( fDylibID != NULL ) {
                return (char*)fDylibID + fDylibID->dylib.name.offset;
        }
        return NULL;
}

// test if this image is re-exported through parent (the image that loaded this one)
bool ImageLoaderMachO::isSubframeworkOf(const LinkContext& context, const ImageLoader* parent) const
{
        if ( fReExportThruFramework != NULL ) {
                // need to match LC_SUB_FRAMEWORK string against the leaf name of the install location of parent...
                const char* parentInstallPath = parent->getInstallPath();
                if ( parentInstallPath != NULL ) {
                        const char* lastSlash = strrchr(parentInstallPath, '/');
                        if ( lastSlash != NULL ) {
                                if ( strcmp(&lastSlash[1], fReExportThruFramework) == 0 )
                                        return true;
                                if ( context.imageSuffix != NULL ) {
                                        // when DYLD_IMAGE_SUFFIX is used, lastSlash string needs imageSuffix removed from end
                                        char reexportAndSuffix[strlen(context.imageSuffix)+strlen(fReExportThruFramework)+1];
                                        strcpy(reexportAndSuffix, fReExportThruFramework);
                                        strcat(reexportAndSuffix, context.imageSuffix);
                                        if ( strcmp(&lastSlash[1], reexportAndSuffix) == 0 )
                                                return true;
                                }
                        }
                }
        }
        return false;
}

// test if child is re-exported 
bool ImageLoaderMachO::hasSubLibrary(const LinkContext& context, const ImageLoader* child) const
{
        if ( fHasSubLibraries ) {
                // need to match LC_SUB_LIBRARY string against the leaf name (without extension) of the install location of child...
                const char* childInstallPath = child->getInstallPath();
                if ( childInstallPath != NULL ) {
                        const char* lastSlash = strrchr(childInstallPath, '/');
                        if ( lastSlash != NULL ) {
                                const char* firstDot = strchr(lastSlash, '.');
                                int len;
                                if ( firstDot == NULL )
                                        len = strlen(lastSlash);
                                else
                                        len = firstDot-lastSlash-1;
                                char childLeafName[len+1];
                                strncpy(childLeafName, &lastSlash[1], len);
                                childLeafName[len] = '\0';
                                const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
                                const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
                                const struct load_command* cmd = cmds;
                                for (uint32_t i = 0; i < cmd_count; ++i) {
                                        switch (cmd->cmd) {
                                                case LC_SUB_LIBRARY:
                                                        {
                                                                const struct sub_library_command* lib = (struct sub_library_command*)cmd;
                                                                const char* aSubLibName = (char*)cmd + lib->sub_library.offset;
                                                                if ( strcmp(aSubLibName, childLeafName) == 0 )
                                                                        return true;
                                                                if ( context.imageSuffix != NULL ) {
                                                                        // when DYLD_IMAGE_SUFFIX is used, childLeafName string needs imageSuffix removed from end
                                                                        char aSubLibNameAndSuffix[strlen(context.imageSuffix)+strlen(aSubLibName)+1];
                                                                        strcpy(aSubLibNameAndSuffix, aSubLibName);
                                                                        strcat(aSubLibNameAndSuffix, context.imageSuffix);
                                                                        if ( strcmp(aSubLibNameAndSuffix, childLeafName) == 0 )
                                                                                return true;
                                                                }
                                                        }
                                                        break;
                                        }
                                        cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
                                }
                        }
                }
        }
        if ( fHasSubUmbrella ) {
                // need to match LC_SUB_UMBRELLA string against the leaf name of install location of child...
                const char* childInstallPath = child->getInstallPath();
                if ( childInstallPath != NULL ) {
                        const char* lastSlash = strrchr(childInstallPath, '/');
                        if ( lastSlash != NULL ) {
                                const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
                                const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
                                const struct load_command* cmd = cmds;
                                for (uint32_t i = 0; i < cmd_count; ++i) {
                                        switch (cmd->cmd) {
                                                case LC_SUB_UMBRELLA:
                                                        {
                                                                const struct sub_umbrella_command* um = (struct sub_umbrella_command*)cmd;
                                                                const char* aSubUmbrellaName = (char*)cmd + um->sub_umbrella.offset;
                                                                if ( strcmp(aSubUmbrellaName, &lastSlash[1]) == 0 )
                                                                        return true;
                                                                if ( context.imageSuffix != NULL ) {
                                                                        // when DYLD_IMAGE_SUFFIX is used, lastSlash string needs imageSuffix removed from end
                                                                        char umbrellaAndSuffix[strlen(context.imageSuffix)+strlen(aSubUmbrellaName)+1];
                                                                        strcpy(umbrellaAndSuffix, aSubUmbrellaName);
                                                                        strcat(umbrellaAndSuffix, context.imageSuffix);
                                                                        if ( strcmp(umbrellaAndSuffix, &lastSlash[1]) == 0 )
                                                                                return true;
                                                                }
                                                        }
                                                        break;
                                        }
                                        cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
                                }
                        }
                }
        }
        return false;
}

        
void* ImageLoaderMachO::getMain() const
{
        const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        for (unsigned long i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_UNIXTHREAD:
                        {
                        #if __ppc__
                                const ppc_thread_state_t* registers = (ppc_thread_state_t*)(((char*)cmd) + 16);
                                return (void*)registers->srr0;
                        #elif __ppc64__
                                const ppc_thread_state64_t* registers = (ppc_thread_state64_t*)(((char*)cmd) + 16);
                                return (void*)registers->srr0;
                        #elif __i386__
                                const i386_thread_state_t* registers = (i386_thread_state_t*)(((char*)cmd) + 16);
                                return (void*)registers->eip;
                        #else
                                #warning need processor specific code
                        #endif
                        }
                        break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
        return NULL;
}


uint32_t ImageLoaderMachO::doGetDependentLibraryCount()
{
        const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
        uint32_t count = 0;
        const struct load_command* cmd = cmds;
        for (unsigned long i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_LOAD_DYLIB:
                        case LC_LOAD_WEAK_DYLIB:
                                ++count;
                                break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
        return count;
}

void ImageLoaderMachO::doGetDependentLibraries(DependentLibrary libs[])
{
        uint32_t index = 0;
        const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        for (unsigned long i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_LOAD_DYLIB:
                        case LC_LOAD_WEAK_DYLIB:
                        {
                                const struct dylib_command* dylib = (struct dylib_command*)cmd;
                                DependentLibrary* lib = &libs[index++];
                                lib->name = (char*)cmd + dylib->dylib.name.offset;
                                //lib->name = strdup((char*)cmd + dylib->dylib.name.offset);
                                lib->image = NULL;
                                lib->info.checksum = dylib->dylib.timestamp;
                                lib->info.minVersion = dylib->dylib.compatibility_version;
                                lib->info.maxVersion = dylib->dylib.current_version;
                                lib->required = (cmd->cmd == LC_LOAD_DYLIB);
                                lib->checksumMatches = false;
                                lib->isReExported = false;
                        }
                        break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
}

ImageLoader::LibraryInfo ImageLoaderMachO::doGetLibraryInfo()
{
        LibraryInfo info;
        if ( fDylibID != NULL ) {
                info.minVersion = fDylibID->dylib.compatibility_version;
                info.maxVersion = fDylibID->dylib.current_version;
                info.checksum = fDylibID->dylib.timestamp;
        }
        else {
                info.minVersion = 0;
                info.maxVersion = 0;            
                info.checksum = 0;
        }
        return info;
}


uintptr_t ImageLoaderMachO::getRelocBase()
{
        if ( fIsSplitSeg ) {
                // in split segment libraries r_address is offset from first writable segment
                const unsigned int segmentCount = fSegments.size();
                for(unsigned int i=0; i < segmentCount; ++i){
                        Segment* seg = fSegments[i];
                        if ( seg->writeable() ) {
                                return seg->getActualLoadAddress();
                        }
                }
        }
        
        // in non-split segment libraries r_address is offset from first segment
        return fSegments[0]->getActualLoadAddress();
}

#if __ppc__
static inline void otherRelocsPPC(uintptr_t* locationToFix, uint8_t relocationType, uint16_t otherHalf, uintptr_t slide)
{
        // low 16 bits of 32-bit ppc instructions need fixing
        struct ppcInstruction { uint16_t opcode; int16_t immediateValue; };
        ppcInstruction* instruction = (ppcInstruction*)locationToFix;
        //uint32_t before = *((uint32_t*)locationToFix);
        switch ( relocationType )
        {
                case PPC_RELOC_LO16: 
                        instruction->immediateValue = ((otherHalf << 16) | instruction->immediateValue) + slide;
                        break;
                case PPC_RELOC_HI16: 
                        instruction->immediateValue = ((((instruction->immediateValue << 16) | otherHalf) + slide) >> 16);
                        break;
                case PPC_RELOC_HA16: 
                        int16_t signedOtherHalf = (int16_t)(otherHalf & 0xffff);
                        uint32_t temp = (instruction->immediateValue << 16) + signedOtherHalf + slide;
                        if ( (temp & 0x00008000) != 0 )
                                temp += 0x00008000;
                        instruction->immediateValue = temp >> 16;
        }
        //uint32_t after = *((uint32_t*)locationToFix);
        //fprintf(stderr, "dyld: ppc fixup %0p type %d from 0x%08X to 0x%08X\n", locationToFix, relocationType, before, after);
}
#endif

void ImageLoaderMachO::doRebase(const LinkContext& context)
{
        // if prebound and loaded at prebound address, then no need to rebase
        // Note: you might think that the check for allDependentLibrariesAsWhenPreBound() is not needed
        // but it is.  If a dependent library changed, this image's lazy pointers into that library
        // need to be updated (reset back to lazy binding handler).  That work is done most easily
        // here because there is a PPC_RELOC_PB_LA_PTR reloc record for each lazy pointer.
        if ( this->usablePrebinding(context) && this->usesTwoLevelNameSpace() ) {
                // skip rebasing cause prebound and prebinding not disabled
                ++fgImagesWithUsedPrebinding; // bump totals for statistics
                return;
        }
                
        // print why prebinding was not used
        if ( context.verbosePrebinding ) {
                if ( !this->isPrebindable() ) {
                        fprintf(stderr, "dyld: image not prebound, so could not use prebinding in %s\n", this->getPath());
                }
                else if ( fSlide != 0 ) {
                        fprintf(stderr, "dyld: image slid, so could not use prebinding in %s\n", this->getPath());
                }
                else if ( !this->allDependentLibrariesAsWhenPreBound() ) {
                        fprintf(stderr, "dyld: dependent libraries changed, so could not use prebinding in %s\n", this->getPath());
                }
                else if ( !this->usesTwoLevelNameSpace() ){
                        fprintf(stderr, "dyld: image uses flat-namespace so, parts of prebinding ignored %s\n", this->getPath());
                }
                else {
                        fprintf(stderr, "dyld: environment variable disabled use of prebinding in %s\n", this->getPath());
                }
        }

        // if there are __TEXT fixups, temporarily make __TEXT writable
        if ( fTextSegmentWithFixups != NULL ) 
                fTextSegmentWithFixups->tempWritable();

        // cache this value that is used in the following loop
        register const uintptr_t slide = this->fSlide;
        
        // loop through all local (internal) relocation records
        const uintptr_t relocBase = this->getRelocBase();
        const relocation_info* const relocsStart = (struct relocation_info*)(&fLinkEditBase[fDynamicInfo->locreloff]);
        const relocation_info* const relocsEnd = &relocsStart[fDynamicInfo->nlocrel];
        for (const relocation_info* reloc=relocsStart; reloc < relocsEnd; ++reloc) {
                if ( (reloc->r_address & R_SCATTERED) == 0 ) {
                        if ( reloc->r_symbolnum == R_ABS ) {
                                // ignore absolute relocations
                        }
                        else if (reloc->r_length == RELOC_SIZE) {
                                switch(reloc->r_type) {
                                        case GENERIC_RELOC_VANILLA:
                                                *((uintptr_t*)(reloc->r_address + relocBase)) += slide;
                                                break;
                #if __ppc__
                                        case PPC_RELOC_HI16: 
                                        case PPC_RELOC_LO16: 
                                        case PPC_RELOC_HA16: 
                                                // some tools leave object file relocations in linked images
                                                otherRelocsPPC((uintptr_t*)(reloc->r_address + relocBase), reloc->r_type, reloc[1].r_address, slide);
                                                ++reloc; // these relocations come in pairs, skip next
                                                break;
                #endif
                                        default:
                                                throw "unknown local relocation type";
                                }
                        }
                        else {
                                throw "bad local relocation length";
                        }
                }
                else {
                        const struct scattered_relocation_info* sreloc = (struct scattered_relocation_info*)reloc;
                        if (sreloc->r_length == RELOC_SIZE) {
                                uintptr_t* locationToFix = (uintptr_t*)(sreloc->r_address + relocBase);
                                switch(sreloc->r_type) {
                                        case GENERIC_RELOC_VANILLA:
                                                *locationToFix += slide;
                                                break;
                #if __ppc__ || __ppc64__
                                        case PPC_RELOC_PB_LA_PTR:
                                                // should only see these in prebound images, and we got here so prebinding is being ignored
                                                *locationToFix = sreloc->r_value + slide;
                                                break;
                #endif
                #if __ppc__
                                        case PPC_RELOC_HI16: 
                                        case PPC_RELOC_LO16: 
                                        case PPC_RELOC_HA16: 
                                                // Metrowerks compiler sometimes leaves object file relocations in linked images???
                                                ++reloc; // these relocations come in pairs, get next one
                                                otherRelocsPPC(locationToFix, sreloc->r_type, reloc->r_address, slide);
                                                break;
                #endif
                #if __i386__
                                        case GENERIC_RELOC_PB_LA_PTR:
                                                // should only see these in prebound images, and we got here so prebinding is being ignored
                                                *locationToFix = sreloc->r_value + slide;
                                                break;
                #endif
                                        default:
                                                throw "unknown local scattered relocation type";
                                }
                        }
                        else {
                                throw "bad local scattered relocation length";
                        }
                }
        }
        
        // if there were __TEXT fixups, restore write protection
        if ( fTextSegmentWithFixups != NULL ) {
                fTextSegmentWithFixups->setPermissions();
                sys_icache_invalidate((void*)fTextSegmentWithFixups->getActualLoadAddress(), fTextSegmentWithFixups->getSize());
        }
        
        // update stats
        fgTotalRebaseFixups += fDynamicInfo->nlocrel;
}


const struct macho_nlist* ImageLoaderMachO::binarySearchWithToc(const char* key, const char stringPool[], const struct macho_nlist symbols[], 
                                                                                                const struct dylib_table_of_contents toc[], uint32_t symbolCount, uint32_t hintIndex)
{
        int32_t high = symbolCount-1;
        int32_t mid = hintIndex;
        
        // handle out of range hint
        if ( mid >= (int32_t)symbolCount ) {
                mid = symbolCount/2;
                ++ImageLoaderMachO::fgUnhintedBinaryTreeSearchs;
        }
        else {
                ++ImageLoaderMachO::fgHintedBinaryTreeSearchs;
        }

        for (int32_t low = 0; low <= high; mid = (low+high)/2) {
                const uint32_t index = toc[mid].symbol_index;
                const struct macho_nlist* pivot = &symbols[index];
                const char* pivotStr = &stringPool[pivot->n_un.n_strx];
#if LINKEDIT_USAGE_DEBUG
                noteAccessedLinkEditAddress(&toc[mid]);
                noteAccessedLinkEditAddress(pivot);
                noteAccessedLinkEditAddress(pivotStr);
#endif
                int cmp = astrcmp(key, pivotStr);
                if ( cmp == 0 )
                        return pivot;
                if ( cmp > 0 ) {
                        // key > pivot 
                        low = mid + 1;
                }
                else {
                        // key < pivot 
                        high = mid - 1;
                }
        }
        return NULL;
}

const struct macho_nlist* ImageLoaderMachO::binarySearch(const char* key, const char stringPool[], const struct macho_nlist symbols[], uint32_t symbolCount)
{
        ++ImageLoaderMachO::fgUnhintedBinaryTreeSearchs;
        const struct macho_nlist* base = symbols;
        for (uint32_t n = symbolCount; n > 0; n /= 2) {
                const struct macho_nlist* pivot = &base[n/2];
                const char* pivotStr = &stringPool[pivot->n_un.n_strx];
#if LINKEDIT_USAGE_DEBUG
                noteAccessedLinkEditAddress(pivot);
                noteAccessedLinkEditAddress(pivotStr);
#endif
                int cmp = astrcmp(key, pivotStr);
                if ( cmp == 0 )
                        return pivot;
                if ( cmp > 0 ) {
                        // key > pivot 
                        // move base to symbol after pivot
                        base = &pivot[1];
                        --n; 
                }
                else {
                        // key < pivot 
                        // keep same base
                }
        }
        return NULL;
}

const ImageLoader::Symbol* ImageLoaderMachO::findExportedSymbol(const char* name, const void* hint, bool searchReExports, ImageLoader** foundIn) const
{
        const struct macho_nlist* sym = NULL;
        const struct twolevel_hint* theHint = (struct twolevel_hint*)hint;
        if ( fDynamicInfo->tocoff == 0 )
                sym = binarySearch(name, fStrings, &fSymbolTable[fDynamicInfo->iextdefsym], fDynamicInfo->nextdefsym);
        else {
                uint32_t start = fDynamicInfo->nextdefsym;
                if ( theHint != NULL )
                         start = theHint->itoc;
                if ( (theHint == NULL) || (theHint->isub_image == 0) ) {
                        sym = binarySearchWithToc(name, fStrings, fSymbolTable, (dylib_table_of_contents*)&fLinkEditBase[fDynamicInfo->tocoff], 
                                                                                fDynamicInfo->ntoc, start);
                }
        }
        if ( sym != NULL ) {
                if ( foundIn != NULL )
                        *foundIn = (ImageLoader*)this;          
                        
                return (const Symbol*)sym;
        }
        
        if ( searchReExports ) {
                // hint might tell us to try a particular subimage
                if ( (theHint != NULL) && (theHint->isub_image > 0) && (theHint->isub_image <= fLibrariesCount) ) {
                        // isub_image is an index into a list that is sorted non-rexported images first
                        uint32_t index = 0;
                        ImageLoader* target = NULL;
                        // pass one, only look at sub-frameworks
                        for (uint32_t i=0; i < fLibrariesCount; ++i) {
                                DependentLibrary& libInfo =  fLibraries[i];
                                if ( libInfo.isSubFramework && (libInfo.image != NULL)) {
                                        if ( ++index == theHint->isub_image ) {
                                                target = libInfo.image;
                                                break;
                                        }
                                }
                        }
                        if (target != NULL) {
                                // pass two, only look at non-sub-framework-reexports
                                for (uint32_t i=0; i < fLibrariesCount; ++i) {
                                        DependentLibrary& libInfo =  fLibraries[i];
                                        if ( libInfo.isReExported && !libInfo.isSubFramework && (libInfo.image != NULL) ) {
                                                if ( ++index == theHint->isub_image ) {
                                                        target = libInfo.image;
                                                        break;
                                                }
                                        }
                                }
                        }
                        if (target != NULL) {
                                const Symbol* result = target->findExportedSymbol(name, NULL, searchReExports, foundIn);
                                if ( result != NULL )
                                        return result;
                        }
                }
                
                // hint failed, try all sub images
                // pass one, only look at sub-frameworks
                for(unsigned int i=0; i < fLibrariesCount; ++i){
                        DependentLibrary& libInfo =  fLibraries[i];
                        if ( (libInfo.image != NULL) && libInfo.isSubFramework ) {
                                const Symbol* result = libInfo.image->findExportedSymbol(name, NULL, searchReExports, foundIn);
                                if ( result != NULL )
                                        return result;
                        }
                }
                // pass two, only look at non-sub-framework-reexports
                for(unsigned int i=0; i < fLibrariesCount; ++i){
                        DependentLibrary& libInfo =  fLibraries[i];
                        if ( (libInfo.image != NULL) && libInfo.isReExported && !libInfo.isSubFramework ) {
                                const Symbol* result = libInfo.image->findExportedSymbol(name, NULL, searchReExports, foundIn);
                                if ( result != NULL )
                                        return result;
                        }
                }
        }
        
        // last change: the hint is wrong (non-zero but actually in this image)
        if ( (theHint != NULL) && (theHint->isub_image != 0) ) {
                sym = binarySearchWithToc(name, fStrings, fSymbolTable, (dylib_table_of_contents*)&fLinkEditBase[fDynamicInfo->tocoff], 
                                                                                fDynamicInfo->ntoc, fDynamicInfo->nextdefsym);
                if ( sym != NULL ) {
                        if ( foundIn != NULL ) 
                                *foundIn = (ImageLoader*)this;
                        return (const Symbol*)sym;
                }
        }

        return NULL;
}


uintptr_t ImageLoaderMachO::getExportedSymbolAddress(const Symbol* sym) const
{
        const struct macho_nlist* nlistSym = (const struct macho_nlist*)sym;
        return nlistSym->n_value + fSlide;
}

ImageLoader::DefinitionFlags ImageLoaderMachO::getExportedSymbolInfo(const Symbol* sym) const
{
        const struct macho_nlist* nlistSym = (const struct macho_nlist*)sym;
        if ( (nlistSym->n_desc & N_WEAK_DEF) != 0 )
                return kWeakDefinition;
        return kNoDefinitionOptions;
}

const char* ImageLoaderMachO::getExportedSymbolName(const Symbol* sym) const
{
        const struct macho_nlist* nlistSym = (const struct macho_nlist*)sym;
        return &fStrings[nlistSym->n_un.n_strx];
}

uint32_t ImageLoaderMachO::getExportedSymbolCount() const
{
        return fDynamicInfo->nextdefsym;
}


const ImageLoader::Symbol* ImageLoaderMachO::getIndexedExportedSymbol(uint32_t index) const
{
        if ( index < fDynamicInfo->nextdefsym ) {
                const struct macho_nlist* sym = &fSymbolTable[fDynamicInfo->iextdefsym + index];
                return (const ImageLoader::Symbol*)sym;
        }
        return NULL;
}


uint32_t ImageLoaderMachO::getImportedSymbolCount() const
{
        return fDynamicInfo->nundefsym;
}


const ImageLoader::Symbol* ImageLoaderMachO::getIndexedImportedSymbol(uint32_t index) const
{
        if ( index < fDynamicInfo->nundefsym ) {
                const struct macho_nlist* sym = &fSymbolTable[fDynamicInfo->iundefsym + index];
                return (const ImageLoader::Symbol*)sym;
        }
        return NULL;
}


ImageLoader::ReferenceFlags ImageLoaderMachO::geImportedSymbolInfo(const ImageLoader::Symbol* sym) const
{
        const struct macho_nlist* nlistSym = (const struct macho_nlist*)sym;
        ImageLoader::ReferenceFlags flags = kNoReferenceOptions;
        if ( ((nlistSym->n_type & N_TYPE) == N_UNDF) && (nlistSym->n_value != 0) )
                flags |= ImageLoader::kTentativeDefinition;
        if ( (nlistSym->n_desc & N_WEAK_REF) != 0 )
                flags |= ImageLoader::kWeakReference;
        return flags;
}


const char* ImageLoaderMachO::getImportedSymbolName(const ImageLoader::Symbol* sym) const
{
        const struct macho_nlist* nlistSym = (const struct macho_nlist*)sym;
        return &fStrings[nlistSym->n_un.n_strx];
}


bool ImageLoaderMachO::getSectionContent(const char* segmentName, const char* sectionName, void** start, size_t* length)
{
        const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        for (uint32_t i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_SEGMENT_COMMAND:
                                {
                                        const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
                                        const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
                                        const struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
                                        for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
                                                if ( (strcmp(sect->segname, segmentName) == 0) && (strcmp(sect->sectname, sectionName) == 0) ) {
                                                        *start = (uintptr_t*)(sect->addr + fSlide);
                                                        *length = sect->size;
                                                        return true;
                                                }
                                        }
                                }
                                break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
        return false;
}


bool ImageLoaderMachO::findSection(const void* imageInterior, const char** segmentName, const char** sectionName, size_t* sectionOffset)
{
        const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        const uintptr_t unslidInteriorAddress = (uintptr_t)imageInterior - this->getSlide();
        for (uint32_t i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_SEGMENT_COMMAND:
                                {
                                        const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
                                        if ( (unslidInteriorAddress >= seg->vmaddr) && (unslidInteriorAddress < (seg->vmaddr+seg->vmsize)) ) {
                                                const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
                                                const struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
                                                for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
                                                        if ((sect->addr <= unslidInteriorAddress) && (unslidInteriorAddress < (sect->addr+sect->size))) {
                                                                if ( segmentName != NULL )
                                                                        *segmentName = sect->segname;
                                                                if ( sectionName != NULL )
                                                                        *sectionName = sect->sectname;
                                                                if ( sectionOffset != NULL )
                                                                        *sectionOffset = unslidInteriorAddress - sect->addr;
                                                                return true;
                                                        }
                                                }
                                        }
                                }
                                break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
        return false;
}


bool ImageLoaderMachO::symbolRequiresCoalescing(const struct macho_nlist* symbol)
{
        // if a define and weak ==> coalesced 
        if ( ((symbol->n_type & N_TYPE) == N_SECT) && ((symbol->n_desc & N_WEAK_DEF) != 0) ) 
                return true;
        // if an undefine and not referencing a weak symbol ==> coalesced
        if ( ((symbol->n_type & N_TYPE) != N_SECT) && ((symbol->n_desc & N_REF_TO_WEAK) != 0) )
                return true;
        
        // regular symbol
        return false;
}


static void __attribute__((noreturn)) throwSymbolNotFound(const char* symbol, const char* referencedFrom, const char* expectedIn)
{
        const char* formatString = "Symbol not found: %s\n  Referenced from: %s\n  Expected in: %s\n";
        char buf[strlen(symbol)+strlen(referencedFrom)+strlen(expectedIn)+strlen(formatString)];
        sprintf(buf, formatString, symbol, referencedFrom, expectedIn);
        throw strdup(buf);  // this is a leak if exception doesn't halt program
}

uintptr_t ImageLoaderMachO::resolveUndefined(const LinkContext& context, const struct macho_nlist* undefinedSymbol, bool twoLevel, ImageLoader** foundIn)
{
        const char* symbolName = &fStrings[undefinedSymbol->n_un.n_strx];

        if ( context.bindFlat || !twoLevel ) {
                // flat lookup
                const Symbol* sym;
                if ( context.flatExportFinder(symbolName, &sym, foundIn) )
                        return (*foundIn)->getExportedSymbolAddress(sym);
                // if a bundle is loaded privately the above will not find its exports
                if ( this->isBundle() && this->hasHiddenExports() ) {
                        // look in self for needed symbol
                        sym = this->findExportedSymbol(symbolName, NULL, false, foundIn);
                        if ( sym != NULL )
                                return (*foundIn)->getExportedSymbolAddress(sym);
                }
                if ( ((undefinedSymbol->n_type & N_PEXT) != 0) || ((undefinedSymbol->n_type & N_TYPE) == N_SECT) ) {
                        // could be a multi-module private_extern internal reference
                        // the static linker squirrels away the target address in n_value
                        uintptr_t addr = undefinedSymbol->n_value + this->fSlide;
                        *foundIn = this;
                        return addr;
                }
                if ( (undefinedSymbol->n_desc & N_WEAK_REF) != 0 ) {
                        // definition can't be found anywhere
                        // if reference is weak_import, then it is ok, just return 0
                        return 0;
                }
                throwSymbolNotFound(symbolName, this->getPath(), "flat namespace");
        }
        else {
                // symbol requires searching images with coalesced symbols
                if ( this->needsCoalescing() && symbolRequiresCoalescing(undefinedSymbol) ) {
                        const Symbol* sym;
                        if ( context.coalescedExportFinder(symbolName, &sym, foundIn) )
                                return (*foundIn)->getExportedSymbolAddress(sym);
                        //throwSymbolNotFound(symbolName, this->getPath(), "coalesced namespace");
                        //fprintf(stderr, "dyld: coalesced symbol %s not found in any coalesced image, falling back to two-level lookup", symbolName);
                }
                
                // two level lookup
                void* hint = NULL;
                ImageLoader* target = NULL;
                uint8_t ord = GET_LIBRARY_ORDINAL(undefinedSymbol->n_desc);
                if ( ord == EXECUTABLE_ORDINAL ) {
                        target = context.mainExecutable;
                }
                else if ( ord == SELF_LIBRARY_ORDINAL ) {
                        target = this;
                }
                else if ( ord == DYNAMIC_LOOKUP_ORDINAL ) {
                        // rnielsen: HACKHACK
                        // flat lookup
                        const Symbol* sym;
                        if ( context.flatExportFinder(symbolName, &sym, foundIn) )
                                return (*foundIn)->getExportedSymbolAddress(sym);
                        // no image has exports this symbol
                        // either report error or hope ZeroLink can just-in-time load an image
                        context.undefinedHandler(symbolName);
                        // try looking again
                        if ( context.flatExportFinder(symbolName, &sym, foundIn) )
                                return (*foundIn)->getExportedSymbolAddress(sym);
                        
                        throwSymbolNotFound(symbolName, this->getPath(), "dynamic lookup");
                }
                else if ( ord <= fLibrariesCount ) {
                        DependentLibrary& libInfo = fLibraries[ord-1];
                        target = libInfo.image;
                        if ( (target == NULL) && (((undefinedSymbol->n_desc & N_WEAK_REF) != 0) || !libInfo.required) ) {
                                // if target library not loaded and reference is weak or library is weak return 0
                                return 0;
                        }
                }
                else {
                        throw "corrupt binary, library ordinal too big";
                }
                
                if ( target == NULL ) {
                        fprintf(stderr, "resolveUndefined(%s) in %s\n", symbolName, this->getPath());
                        throw "symbol not found";
                }
                
                // interpret hint
                if ( fTwoLevelHints != NULL ) {
                        uint32_t symIndex = undefinedSymbol - fSymbolTable;
                        int32_t undefinedIndex = symIndex - fDynamicInfo->iundefsym;
                        if ( (undefinedIndex >= 0) && ((uint32_t)undefinedIndex < fDynamicInfo->nundefsym) ) {
                                const struct twolevel_hint* hints = (struct twolevel_hint*)(&fLinkEditBase[fTwoLevelHints->offset]);
                                const struct twolevel_hint* theHint = &hints[undefinedIndex];
                                hint = (void*)theHint;
                        }
                }
                
                const Symbol* sym = target->findExportedSymbol(symbolName, hint, true, foundIn);
                if ( sym!= NULL ) {
                        return (*foundIn)->getExportedSymbolAddress(sym);
                }
                else if ( (undefinedSymbol->n_type & N_PEXT) != 0 ) {
                        // don't know why the static linker did not eliminate the internal reference to a private extern definition
                        *foundIn = this;
                        return undefinedSymbol->n_value + fSlide;
                }
                else if ( (undefinedSymbol->n_desc & N_WEAK_REF) != 0 ) {
                        // if definition not found and reference is weak return 0
                        return 0;
                }
                
                // nowhere to be found
                throwSymbolNotFound(symbolName, this->getPath(), target->getPath());
        }
}

void ImageLoaderMachO::doBindExternalRelocations(const LinkContext& context, bool onlyCoalescedSymbols)
{
        const uintptr_t relocBase = this->getRelocBase();
        const bool twoLevel = this->usesTwoLevelNameSpace();
        const bool prebound = this->isPrebindable();
        
        // if there are __TEXT fixups, temporarily make __TEXT writable
        if ( fTextSegmentWithFixups != NULL ) 
                fTextSegmentWithFixups->tempWritable();

        // cache last lookup
        const struct macho_nlist*       lastUndefinedSymbol = 0;
        uintptr_t                                       symbolAddr = 0;
        ImageLoader*                            image = NULL;
        
        // loop through all external relocation records and bind each
        const relocation_info* const relocsStart = (struct relocation_info*)(&fLinkEditBase[fDynamicInfo->extreloff]);
        const relocation_info* const relocsEnd = &relocsStart[fDynamicInfo->nextrel];
        for (const relocation_info* reloc=relocsStart; reloc < relocsEnd; ++reloc) {
                if (reloc->r_length == RELOC_SIZE) {
                        switch(reloc->r_type) {
                                case GENERIC_RELOC_VANILLA:
                                        {
                                                const struct macho_nlist* undefinedSymbol = &fSymbolTable[reloc->r_symbolnum];
                                                // if only processing coalesced symbols and this one does not require coalesceing, skip to next
                                                if ( onlyCoalescedSymbols && !symbolRequiresCoalescing(undefinedSymbol) )
                                                        continue;
                                                uintptr_t* location = ((uintptr_t*)(reloc->r_address + relocBase));
                                                uintptr_t value = *location;
                                                if ( prebound ) {
                                                        // we are doing relocations, so prebinding was not usable
                                                        // in a prebound executable, the n_value field is set to the address where the symbol was found when prebound
                                                        // so, subtracting that gives the initial displacement which we need to add to the newly found symbol address
                                                        // if mach-o relocation structs had an "addend" field this would not be necessary.
                                                        value -= undefinedSymbol->n_value;
                                                }
                                                // if undefinedSymbol is same as last time, then symbolAddr and image will resolve to the same too
                                                if ( undefinedSymbol != lastUndefinedSymbol ) {
                                                        symbolAddr = this->resolveUndefined(context, undefinedSymbol, twoLevel, &image);
                                                        lastUndefinedSymbol = undefinedSymbol;
                                                }
                                                if ( context.verboseBind ) {
                                                        const char *path = NULL;
                                                        if(NULL != image) {
                                                                path = image->getShortName();
                                                        }
                                                        if(0 == value) {
                                                                fprintf(stderr, "dyld: bind: %s:0x%08lx = %s:%s, *0x%08lx = 0x%08lx\n",
                                                                                this->getShortName(), (uintptr_t)location,
                                                                                path, &fStrings[undefinedSymbol->n_un.n_strx], (uintptr_t)location, symbolAddr);
                                                        }
                                                        else {
                                                                fprintf(stderr, "dyld: bind: %s:0x%08lx = %s:%s, *0x%08lx = 0x%08lx + %ld\n",
                                                                                this->getShortName(), (uintptr_t)location,
                                                                                path, &fStrings[undefinedSymbol->n_un.n_strx], (uintptr_t)location, symbolAddr, value);
                                                        }
                                                }
                                                value += symbolAddr;
                                                *location = value; 
                                        }
                                        break;
                                default:
                                        throw "unknown external relocation type";
                        }
                }
                else {
                        throw "bad external relocation length";
                }
        }
        
        // if there were __TEXT fixups, restore write protection
        if ( fTextSegmentWithFixups != NULL ) {
                fTextSegmentWithFixups->setPermissions();
                sys_icache_invalidate((void*)fTextSegmentWithFixups->getActualLoadAddress(), fTextSegmentWithFixups->getSize());
        }
        
        // update stats
        fgTotalBindFixups += fDynamicInfo->nextrel;
}

const mach_header* ImageLoaderMachO::machHeader() const
{
        return (mach_header*)fMachOData;
}

uintptr_t ImageLoaderMachO::getSlide() const
{
        return fSlide;
}

// hmm. maybe this should be up in ImageLoader??
const void* ImageLoaderMachO::getBaseAddress() const
{
        Segment* seg = fSegments[0];
        return (const void*)seg->getActualLoadAddress();
}


uintptr_t ImageLoaderMachO::doBindLazySymbol(uintptr_t* lazyPointer, const LinkContext& context)
{
        // scan for all non-lazy-pointer sections
        const bool twoLevel = this->usesTwoLevelNameSpace();
        const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        const uint32_t* const indirectTable = (uint32_t*)&fLinkEditBase[fDynamicInfo->indirectsymoff];
        for (uint32_t i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_SEGMENT_COMMAND:
                                {
                                        const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
                                        const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
                                        const struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
                                        for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
                                                const uint8_t type = sect->flags & SECTION_TYPE;
                                                if ( type == S_LAZY_SYMBOL_POINTERS ) {
                                                        const uint32_t pointerCount = sect->size / sizeof(uintptr_t);
                                                        uintptr_t* const symbolPointers = (uintptr_t*)(sect->addr + fSlide);
                                                        if ( (lazyPointer >= symbolPointers) && (lazyPointer < &symbolPointers[pointerCount]) ) {
                                                                const uint32_t indirectTableOffset = sect->reserved1;
                                                                const uint32_t lazyIndex = lazyPointer - symbolPointers;
                                                                uint32_t symbolIndex = indirectTable[indirectTableOffset + lazyIndex];
                                                                if ( symbolIndex != INDIRECT_SYMBOL_ABS && symbolIndex != INDIRECT_SYMBOL_LOCAL ) {
                                                                        ImageLoader *image = NULL;
                                                                        const char *path = NULL;
                                                                        uintptr_t symbolAddr = this->resolveUndefined(context,  &fSymbolTable[symbolIndex], twoLevel, &image);
                                                                        if ( context.verboseBind ) {
                                                                                if(NULL == path && NULL != image) {
                                                                                        path = image->getShortName();
                                                                                }
                                                                                fprintf(stderr, "dyld: bind: %s:%s$%s = %s:%s, *0x%08lx = 0x%08lx\n",
                                                                                                this->getShortName(), &fStrings[fSymbolTable[symbolIndex].n_un.n_strx], "lazy_ptr",
                                                                                                path, &fStrings[fSymbolTable[symbolIndex].n_un.n_strx], (uintptr_t)&symbolPointers[lazyIndex], symbolAddr);
                                                                        }
                                                                        if ( NULL != context.bindingHandler ) {
                                                                                if(NULL == path && NULL != image) {
                                                                                        path = image->getPath();
                                                                                }
                                                                                symbolAddr = (uintptr_t)context.bindingHandler(path, &fStrings[fSymbolTable[symbolIndex].n_un.n_strx], (void *)symbolAddr);
                                                                        }
                                                                        symbolPointers[lazyIndex] = symbolAddr;
                                                                        // update stats
                                                                        fgTotalLazyBindFixups++;
                                                                        return symbolPointers[lazyIndex];
                                                                }
                                                        }
                                                }
                                        }
                                }
                                break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
        throw "lazy pointer not found";
}



void ImageLoaderMachO::doBindIndirectSymbolPointers(const LinkContext& context, BindingLaziness bindness, bool onlyCoalescedSymbols)
{
        // scan for all non-lazy-pointer sections 
        const bool twoLevel = this->usesTwoLevelNameSpace();
        const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        const uint32_t* const indirectTable = (uint32_t*)&fLinkEditBase[fDynamicInfo->indirectsymoff];
        for (uint32_t i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_SEGMENT_COMMAND:
                                {
                                        const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
                                        const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
                                        const struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
                                        for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
                                                const uint8_t type = sect->flags & SECTION_TYPE;
                                                const uint32_t pointerCount = sect->size / sizeof(uintptr_t);
                                                if ( type == S_NON_LAZY_SYMBOL_POINTERS ) {
                                                        if ( (bindness == kLazyOnly) || (bindness == kLazyOnlyNoDependents) )
                                                                continue;
                                                }
                                                else if ( type == S_LAZY_SYMBOL_POINTERS ) {
                                                        // process each symbol pointer in this section
                                                        fgTotalPossibleLazyBindFixups += pointerCount;
                                                        if ( bindness == kNonLazyOnly )
                                                                continue;
                                                }
                                                else {
                                                        continue;
                                                }
                                                const uint32_t indirectTableOffset = sect->reserved1;
                                                uintptr_t* const symbolPointers = (uintptr_t*)(sect->addr + fSlide);
                                                for (uint32_t j=0; j < pointerCount; ++j) {
                                                        uint32_t symbolIndex = indirectTable[indirectTableOffset + j];
                                                        if ( symbolIndex == INDIRECT_SYMBOL_LOCAL) {
                                                                symbolPointers[j] += this->fSlide;
                                                        }
                                                        else if ( symbolIndex == INDIRECT_SYMBOL_ABS) {
                                                                // do nothing since already has absolute address
                                                        }
                                                        else {
                                                                const struct macho_nlist* sym = &fSymbolTable[symbolIndex];
                                                                if ( symbolIndex == 0 ) {
                                                                        // This could be rdar://problem/3534709 
                                                                        if ( ((const macho_header*)fMachOData)->filetype == MH_EXECUTE ) {
                                                                                static bool alreadyWarned = false;
                                                                                if ( (sym->n_type & N_TYPE) != N_UNDF ) {
                                                                                        // The indirect table parallels the (non)lazy pointer sections.  For
                                                                                        // instance, to find info about the fifth lazy pointer you look at the
                                                                                        // fifth entry in the indirect table.  (try otool -Iv on a file).
                                                                                        // The entry in the indirect table contains an index into the symbol table.

                                                                                        // The bug in ld caused the entry in the indirect table to be zero
                                                                                        // (instead of a magic value that means a local symbol).  So, if the
                                                                                        // symbolIndex == 0, we may be encountering the bug, or 0 may be a valid
                                                                                        // symbol table index. The check I put in place is to see if the zero'th
                                                                                        // symbol table entry is an import entry (usually it is a local symbol
                                                                                        // definition).
                                                                                        if ( context.verboseWarnings && !alreadyWarned ) {
                                                                                                fprintf(stderr, "dyld: malformed executable '%s', skipping indirect symbol to %s\n",
                                                                                                                this->getPath(), &fStrings[sym->n_un.n_strx]);
                                                                                                alreadyWarned = true;
                                                                                        }
                                                                                        continue;
                                                                                }
                                                                        }
                                                                }
                                                                ImageLoader *image = NULL;
                                                                // if only processing coalesced symbols and this one does not require coalesceing, skip to next
                                                                if ( onlyCoalescedSymbols && !symbolRequiresCoalescing(sym) )
                                                                        continue;
                                                                uintptr_t symbolAddr;
                                                                        symbolAddr = resolveUndefined(context, sym, twoLevel, &image);
                                                                if ( context.verboseBind ) {
                                                                        const char *path = NULL;
                                                                        if(NULL != image) {
                                                                                path = image->getShortName();
                                                                        }
                                                                        const char *typeName;
                                                                        if ( type == S_LAZY_SYMBOL_POINTERS ) {
                                                                                typeName = "lazy_ptr";
                                                                        }
                                                                        else {
                                                                                typeName = "non_lazy_ptr";
                                                                        }
                                                                        fprintf(stderr, "dyld: bind: %s:%s$%s = %s:%s, *0x%08lx = 0x%08lx\n",
                                                                                        this->getShortName(), &fStrings[sym->n_un.n_strx], typeName,
                                                                                        path, &fStrings[sym->n_un.n_strx], (uintptr_t)&symbolPointers[j], symbolAddr);
                                                                }
                                                                symbolPointers[j] = symbolAddr;
                                                        }
                                                }
                                                // update stats
                                                fgTotalBindFixups += pointerCount;
                                        }
                                }
                                break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
}

/*
 * The address of these symbols are written in to the (__DATA,__dyld) section
 * at the following offsets:
 *      at offset 0     stub_binding_helper_interface
 *      at offset 4     _dyld_func_lookup
 *      at offset 8     start_debug_thread
 * The 'C' types (if any) for these symbols are ignored here and all are
 * declared as longs so the assignment of their address in to the section will
 * not require a cast.  stub_binding_helper_interface is really a label in the
 * assembly code interface for the stub binding.  It does not have a meaningful 
 * 'C' type.  _dyld_func_lookup is the routine in dyld_libfuncs.c.
 * start_debug_thread is the routine in debug.c.
 *
 * For ppc the image's stub_binding_binding_helper is read from:
 *      at offset 20    the image's stub_binding_binding_helper address
 * and saved into to the image structure.
 */
struct DATAdyld {
        void*   dyldLazyBinder;         // filled in at launch by dyld to point into dyld to &stub_binding_helper_interface
        void*   dyldFuncLookup;         // filled in at launch by dyld to point into dyld to &_dyld_func_lookup
        void*   startDebugThread;   // debugger interface ???
        void*   debugPort;                      // debugger interface ???
        void*   debugThread;            // debugger interface ???
        void*   stubBindHelper;         // filled in at static link time to point to stub helper in image
        void*   coreDebug;                      // ???
};

// These are defined in dyldStartup.s
extern "C" void stub_binding_helper();
extern "C" bool dyld_func_lookup(const char* name, uintptr_t* address);


void ImageLoaderMachO::setupLazyPointerHandler()
{
        if ( fDATAdyld != NULL ) {
                struct DATAdyld* dd = (struct DATAdyld*)(fDATAdyld->addr + fSlide);
                if ( fDATAdyld->size > offsetof(DATAdyld, dyldLazyBinder) ) {
                        if ( dd->dyldLazyBinder != (void*)&stub_binding_helper )
                                dd->dyldLazyBinder = (void*)&stub_binding_helper;
                }
                if ( fDATAdyld->size > offsetof(DATAdyld, dyldFuncLookup) ) {
                        if ( dd->dyldFuncLookup != (void*)&dyld_func_lookup )
                                dd->dyldFuncLookup = (void*)&dyld_func_lookup;
                }
                //if ( fDATAdyld->size > offsetof(DATAdyld, startDebugThread) ) 
                //      dd->startDebugThread = &start_debug_thread;
#ifdef __ppc__
                //if ( fDATAdyld->size > offsetof(DATAdyld, stubBindHelper) )
                //      save = dd->stubBindHelper;      
#endif
        }
}

bool ImageLoaderMachO::usablePrebinding(const LinkContext& context) const
{
        // if prebound and loaded at prebound address, and all libraries are same as when this was prebound, then no need to bind
        if ( this->isPrebindable() && this->allDependentLibrariesAsWhenPreBound() && (this->getSlide() == 0) ) {
                // allow environment variables to disable prebinding
                if ( context.bindFlat )
                        return false;
                switch ( context.prebindUsage ) {
                        case kUseAllPrebinding:
                                return true;
                        case kUseSplitSegPrebinding:
                                return this->fIsSplitSeg;
                        case kUseAllButAppPredbinding:
                                return (this != context.mainExecutable);
                        case kUseNoPrebinding:
                                return false;
                }
        }
        return false;
}

void ImageLoaderMachO::doBind(const LinkContext& context, BindingLaziness bindness)
{
        // set dyld entry points in image
        this->setupLazyPointerHandler();

        // if prebound and loaded at prebound address, and all libraries are same as when this was prebound, then no need to bind
        // note: flat-namespace binaries need to be imports rebound (even if correctly prebound)
        if ( this->usablePrebinding(context) && this->usesTwoLevelNameSpace() ) {
                // if image has coalesced symbols, then these need to be rebound
                if ( this->needsCoalescing() ) {
                        this->doBindExternalRelocations(context, true);
                        this->doBindIndirectSymbolPointers(context, kLazyAndNonLazy, true);
                }
                // skip binding because prebound and prebinding not disabled
                return;
        }
        
        // values bound by name are stored two different ways in mach-o
        switch (bindness) {
                case kNonLazyOnly:
                case kLazyAndNonLazy:
                        // external relocations are used for data initialized to external symbols
                        this->doBindExternalRelocations(context, false);
                        break;
                case kLazyOnly:
                case kLazyOnlyNoDependents:
                        break;
        }
        // "indirect symbols" are used for code references to external symbols
        this->doBindIndirectSymbolPointers(context, bindness, false);
}



void ImageLoaderMachO::doImageInit(const LinkContext& context)
{
        if ( fDashInit != NULL ) {
                Initializer func = (Initializer)(fDashInit->init_address + fSlide);
                if ( context.verboseInit )
                        fprintf(stderr, "dyld: calling -init function 0x%p in %s\n", func, this->getPath());
                func(context.argc, context.argv, context.envp, context.apple);
        }
}

void ImageLoaderMachO::doModInitFunctions(const LinkContext& context)
{
        if ( fModInitSection != NULL ) {
                Initializer* inits = (Initializer*)(fModInitSection->addr + fSlide);
                const uint32_t count = fModInitSection->size / sizeof(uintptr_t);
                for (uint32_t i=0; i < count; ++i) {
                        Initializer func = inits[i];
                        if ( context.verboseInit )
                                fprintf(stderr, "dyld: calling initializer function %p in %s\n", func, this->getPath());
                        func(context.argc, context.argv, context.envp, context.apple);
                }
        }
}


void ImageLoaderMachO::doInitialization(const LinkContext& context)
{
        // mach-o has -init and static initializers
        doImageInit(context);
        doModInitFunctions(context);
}

bool ImageLoaderMachO::needsInitialization()
{
        return ( (fDashInit != NULL) || (fModInitSection != NULL) );
}


bool ImageLoaderMachO::needsTermination()
{
        return ( fModTermSection != NULL );
}

bool ImageLoaderMachO::hasImageNotification()
{
        return ( fImageNotifySection != NULL );
}


void ImageLoaderMachO::doTermination(const LinkContext& context)
{
        if ( fModTermSection != NULL ) {
                Terminator* terms = (Terminator*)(fModTermSection->addr + fSlide);
                const uint32_t count = fModTermSection->size / sizeof(uintptr_t);
                for (uint32_t i=count; i > 0; --i) {
                        Terminator func = terms[i-1];
                        if ( context.verboseInit )
                                fprintf(stderr, "dyld: calling terminaton function %p in %s\n", func, this->getPath());
                        func();
                }
        }
}

void ImageLoaderMachO::doNotification(enum dyld_image_mode mode, uint32_t infoCount, const struct dyld_image_info info[])
{
        if ( fImageNotifySection != NULL ) {
                dyld_image_notifier* notes = (dyld_image_notifier*)(fImageNotifySection->addr + fSlide);
                const uint32_t count = fImageNotifySection->size / sizeof(uintptr_t);
                for (uint32_t i=count; i > 0; --i) {
                        dyld_image_notifier func = notes[i-1];
                        func(mode, infoCount, info);
                }
        }
}

void ImageLoaderMachO::printStatistics(unsigned int imageCount)
{
        ImageLoader::printStatistics(imageCount);
        fprintf(stderr, "total hinted binary tree searches:    %d\n", fgHintedBinaryTreeSearchs);
        fprintf(stderr, "total unhinted binary tree searches:  %d\n", fgUnhintedBinaryTreeSearchs);
        
#if LINKEDIT_USAGE_DEBUG
        fprintf(stderr, "linkedit pages accessed (%lu):\n", sLinkEditPageBuckets.size());
#endif  
}

void ImageLoaderMachO::doPrebinding(const LinkContext& context, time_t timestamp, uint8_t* fileToPrebind)
{
        // update __DATA segment
        this->applyPrebindingToDATA(fileToPrebind);
        
        // update load commands 
        this->applyPrebindingToLoadCommands(context, fileToPrebind, timestamp);
        
        // update symbol table  
        this->applyPrebindingToLinkEdit(context, fileToPrebind);
}

void ImageLoaderMachO::applyPrebindingToDATA(uint8_t* fileToPrebind)
{
        const unsigned int segmentCount = fSegments.size();
        for(unsigned int i=0; i < segmentCount; ++i) {
                SegmentMachO* seg = (SegmentMachO*)fSegments[i];
                if ( seg->writeable() ) {
                        memcpy(&fileToPrebind[seg->fFileOffset], (void*)seg->getActualLoadAddress(), seg->fFileSize);
                }
        }
}

void ImageLoaderMachO::applyPrebindingToLoadCommands(const LinkContext& context, uint8_t* fileToPrebind, time_t timestamp)
{
        macho_header* mh = (macho_header*)fileToPrebind;
        const uint32_t cmd_count = mh->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fileToPrebind[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        for (uint32_t i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_LOAD_DYLIB:
                        case LC_LOAD_WEAK_DYLIB:
                                {
                                        // update each dylib load command with the timestamp of the target dylib
                                        struct dylib_command* dylib  = (struct dylib_command*)cmd;
                                        const char* name = (char*)cmd + dylib->dylib.name.offset;
                                        for (const DependentLibrary* dl=fLibraries; dl < &fLibraries[fLibrariesCount]; dl++) {
                                                if (strcmp(dl->name, name) == 0 ) {
                                                        // found matching DependentLibrary for this load command
                                                        ImageLoaderMachO* targetImage = (ImageLoaderMachO*)(dl->image); // !!! assume only mach-o images are prebound
                                                        if ( ! targetImage->isPrebindable() )
                                                                throw "dependent dylib is not prebound";
                                                        // if the target is currently being re-prebound then its timestamp will be the same as this one
                                                        if ( ! targetImage->usablePrebinding(context) ) {
                                                                dylib->dylib.timestamp = timestamp;
                                                        }
                                                        else {
                                                                // otherwise dependent library is already correctly prebound, so use its checksum
                                                                dylib->dylib.timestamp = targetImage->doGetLibraryInfo().checksum;
                                                        }
                                                        break;
                                                }
                                        }
                                }
                                break;
                        case LC_ID_DYLIB:
                                {
                                        // update the ID of this library with the new timestamp
                                        struct dylib_command* dylib  = (struct dylib_command*)cmd;
                                        dylib->dylib.timestamp = timestamp;
                                }
                                break;
                        case LC_SEGMENT_COMMAND:
                                // if dylib was rebased, update segment commands
                                if ( fSlide != 0 ) {
                                        struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
                                        seg->vmaddr += fSlide;
                                        struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
                                        struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
                                        for (struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
                                                sect->addr += fSlide;
                                        }
                                }
                                break;
                        case LC_ROUTINES_COMMAND:
                                // if dylib was rebased, update -init command
                                if ( fSlide != 0 ) {
                                        struct macho_routines_command* routines = (struct macho_routines_command*)cmd;
                                        routines->init_address += fSlide;
                                }
                                break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }       
}

void ImageLoaderMachO::applyPrebindingToLinkEdit(const LinkContext& context, uint8_t* fileToPrebind)
{
        // In prebound images, the n_value of the symbol table entry for is the prebound address
        // This is needed when prebinding can't be used, to back solve for any possible addend in non-lazy pointers
        const char* stringPool = NULL;
        struct macho_nlist* symbolTable = NULL;
        const struct dysymtab_command* dysymtab = NULL;
        
        // get symbol table info
        macho_header* mh = (macho_header*)fileToPrebind;
        const uint32_t cmd_count = mh->ncmds;
        const struct load_command* const cmds = (struct load_command*)&fileToPrebind[sizeof(macho_header)];
        const struct load_command* cmd = cmds;
        for (uint32_t i = 0; i < cmd_count; ++i) {
                switch (cmd->cmd) {
                        case LC_SYMTAB:
                                {
                                        const struct symtab_command* symtab = (struct symtab_command*)cmd;
                                        stringPool = (const char*)&fileToPrebind[symtab->stroff];
                                        symbolTable = (struct macho_nlist*)(&fileToPrebind[symtab->symoff]);
                                }
                                break;
                        case LC_DYSYMTAB:
                                dysymtab = (struct dysymtab_command*)cmd;
                                break;
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }       

        // walk all imports and re-resolve their n_value (needed incase prebinding is invalid)
        struct macho_nlist* lastImport = &symbolTable[dysymtab->iundefsym+dysymtab->nundefsym];
        for (struct macho_nlist* entry = &symbolTable[dysymtab->iundefsym]; entry < lastImport; ++entry) {
                ImageLoader* dummy;
                entry->n_value = this->resolveUndefined(context, entry, this->usesTwoLevelNameSpace(), &dummy);
        }
        
        // walk all exports and slide their n_value
        struct macho_nlist* lastExport = &symbolTable[dysymtab->iextdefsym+dysymtab->nextdefsym];
        for (struct macho_nlist* entry = &symbolTable[dysymtab->iextdefsym]; entry < lastExport; ++entry) {
                entry->n_value += fSlide;
        }

        // walk all local symbols and slide their n_value
        struct macho_nlist* lastLocal = &symbolTable[dysymtab->ilocalsym+dysymtab->nlocalsym];
        for (struct macho_nlist* entry = &symbolTable[dysymtab->ilocalsym]; entry < lastLocal; ++entry) {
                if ( (entry->n_type & N_TYPE) == N_SECT )
                        entry->n_value += fSlide;
        }
        
        // walk all local relocations and reset every PPC_RELOC_PB_LA_PTR r_value
        relocation_info* const relocsStart = (struct relocation_info*)(&fileToPrebind[dysymtab->locreloff]);
        relocation_info* const relocsEnd = &relocsStart[dysymtab->nlocrel];
        for (relocation_info* reloc=relocsStart; reloc < relocsEnd; ++reloc) {
                if ( (reloc->r_address & R_SCATTERED) != 0 ) {
                        struct scattered_relocation_info* sreloc = (struct scattered_relocation_info*)reloc;
                        if (sreloc->r_length == RELOC_SIZE) {
                                switch(sreloc->r_type) {
                #if __ppc__ || __ppc64__
                                        case PPC_RELOC_PB_LA_PTR:
                #elif __i386__
                                        case GENERIC_RELOC_PB_LA_PTR:
                #else
                        #error unknown architecture
                #endif
                                                sreloc->r_value += fSlide;
                                                break;
                                }
                        }
                }
        }

}


SegmentMachO::SegmentMachO(const struct macho_segment_command* cmd, ImageLoaderMachO* image, const uint8_t* fileData)
 : fImage(image), fSize(cmd->vmsize), fFileSize(cmd->filesize), fFileOffset(cmd->fileoff), fPreferredLoadAddress(cmd->vmaddr), 
        fVMProtection(cmd->initprot), fHasFixUps(false), fUnMapOnDestruction(false)
{
        strncpy(fName, cmd->segname, 16);
        fName[16] = '\0';
        // scan sections for fix-up bit
        const struct macho_section* const sectionsStart = (struct macho_section*)((char*)cmd + sizeof(struct macho_segment_command));
        const struct macho_section* const sectionsEnd = &sectionsStart[cmd->nsects];
        for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
                if ( (sect->flags & (S_ATTR_EXT_RELOC | S_ATTR_LOC_RELOC)) != 0 )
                        fHasFixUps = true;
        }
}

SegmentMachO::~SegmentMachO()
{
        if ( fUnMapOnDestruction ) {
                //fprintf(stderr, "unmapping segment %s at 0x%08lX\n", getName(), getActualLoadAddress());
                munmap((void*)(this->getActualLoadAddress()), this->getSize());
        }
}

const ImageLoader* SegmentMachO::getImage()
{
        return fImage;
}

const char* SegmentMachO::getName()
{
        return fName;
}

uintptr_t SegmentMachO::getSize()
{
        return fSize;
}

uintptr_t SegmentMachO::getFileSize()
{
        return fFileSize;
}

uintptr_t SegmentMachO::getFileOffset()
{
        return fFileOffset;
}

bool SegmentMachO::readable()
{
        return ( (fVMProtection & VM_PROT_READ) != 0);
}

bool SegmentMachO::writeable()
{
        return ((fVMProtection & VM_PROT_WRITE) != 0);
}

bool SegmentMachO::executable()
{
        return ((fVMProtection & VM_PROT_EXECUTE) != 0);
}

bool SegmentMachO::unaccessible()
{
        return (fVMProtection == 0);
}

bool SegmentMachO::hasFixUps()
{
        return fHasFixUps;
}

uintptr_t SegmentMachO::getActualLoadAddress()
{
        return fPreferredLoadAddress + fImage->fSlide;
}

uintptr_t SegmentMachO::getPreferredLoadAddress()
{
        return fPreferredLoadAddress;
}

bool SegmentMachO::hasPreferredLoadAddress()
{
        return (fPreferredLoadAddress != 0);
}

void SegmentMachO::setUnMapWhenDestructed(bool unmap)
{
        fUnMapOnDestruction = unmap;
}

static uint32_t *buildCRCTable(void)
{
        uint32_t *table = new uint32_t[256];
        uint32_t p = 0xedb88320UL;  // standard CRC-32 polynomial

        for (unsigned int i = 0; i < 256; i++) {
                uint32_t c = i;
                for (unsigned int j = 0; j < 8; j++) {
                        if ( c & 1 ) c = p ^ (c >> 1);
                        else c = c >> 1;
                }
                table[i] = c;
        }

        return table;
}

uint32_t SegmentMachO::crc32()
{
        if ( !readable() ) return 0;

        static uint32_t *crcTable = NULL;
        if ( !crcTable ) crcTable = buildCRCTable();
        
        uint32_t crc = ~(uint32_t)0;
        uint8_t *p = (uint8_t *)getActualLoadAddress(); 
        uint8_t *end = p + getSize();
        while ( p < end ) {
                crc = crcTable[(crc & 0xff) ^ (*p++)] ^ (crc >> 8);
        }
        return crc ^ ~(uint32_t)0;
}