objc4-235.tar.gz

[apple/objc4.git] / runtime / objc-runtime.m

/*
 * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
 * 
 * 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@
 */
/***********************************************************************
* objc-runtime.m
* Copyright 1988-1996, NeXT Software, Inc.
* Author:       s. naroff
*
**********************************************************************/

/***********************************************************************
* Imports.
**********************************************************************/


#include <mach-o/ldsyms.h>
#include <mach-o/dyld.h>
#include <mach/vm_statistics.h>

// project headers first, otherwise we get the installed ones
#import "objc-class.h"
#import <objc/objc-runtime.h>
#import <objc/hashtable2.h>
#import "maptable.h"
#import "objc-private.h"
#import <objc/Object.h>
#import <objc/Protocol.h>

#include <sys/time.h>
#include <sys/resource.h>

OBJC_EXPORT Class _objc_getNonexistentClass(void);


OBJC_EXPORT Class getOriginalClassForPosingClass(Class);


/***********************************************************************
* Constants and macros internal to this module.
**********************************************************************/

/* Turn on support for literal string objects. */
#define LITERAL_STRING_OBJECTS

/***********************************************************************
* Types internal to this module.
**********************************************************************/

typedef struct _objc_unresolved_category
{
    struct _objc_unresolved_category *  next;
    struct objc_category *                      cat;
    long                                        version;
    int                                         bindme;
} _objc_unresolved_category;

typedef struct _PendingClass
{
    struct objc_class * *                       ref;
    struct objc_class *                 classToSetUp;
    const char *                nameof_superclass;
    int                 version;
    struct _PendingClass *      next;
} PendingClass;

/***********************************************************************
* Exports.
**********************************************************************/

// Function called after class has been fixed up (MACH only)
void            (*callbackFunction)(Class, const char *) = 0;

// Lock for class hashtable
OBJC_DECLARE_LOCK (classLock);

// Condition for logging load progress
static int LaunchingDebug = -1; // env "LaunchingDebug"
static int PrintBinding = -1;    // env "OBJC_PRINT_BIND"

// objc's key for pthread_getspecific
pthread_key_t _objc_pthread_key;

// Is every library up to now prebound?
static int all_modules_prebound = 0;

/***********************************************************************
* Function prototypes internal to this module.
**********************************************************************/

static unsigned                 classHash                                                       (void * info, struct objc_class * data);
static int                              classIsEqual                                            (void * info, struct objc_class * name, struct objc_class * cls);
static int                              _objc_defaultClassHandler                       (const char * clsName);
static void                             _objcTweakMethodListPointerForClass     (struct objc_class * cls);
static void                             _objc_add_category_flush_caches(struct objc_class * cls, struct objc_category * category, int version);
static void                             _objc_add_category(struct objc_class * cls, struct objc_category * category, int version);
static void                             _objc_register_category                         (struct objc_category * cat, long version, int bindme);
static void                             _objc_add_categories_from_image         (header_info * hi);
static const header_info * _headerForClass                                      (struct objc_class * cls);
static PendingClass *   newPending                                                      (void);
static NXMapTable *             pendingClassRefsMapTable                        (void);
static void             _objc_add_classes_from_image            (NXHashTable * clsHash, header_info * hi);
static void                             _objc_fixup_string_objects_for_image(header_info * hi);
static void                             _objc_map_class_refs_for_image          (header_info * hi);
static void                             map_selrefs                                                     (SEL * sels, unsigned int cnt);
static void                             map_method_descs                                        (struct objc_method_description_list * methods);
static void                             _objc_fixup_protocol_objects_for_image  (header_info * hi);
static void                             _objc_bindModuleContainingCategory(Category cat);
static void                             _objc_fixup_selector_refs                       (const header_info * hi);
static void                             _objc_call_loads_for_image                      (header_info * header);
static void                             _objc_checkForPendingClassReferences           (struct objc_class *     cls);
static void                             _objc_map_image(headerType *mh, unsigned long   vmaddr_slide);
static void                             _objc_unmap_image(headerType *mh, unsigned long vmaddr_slide);

/***********************************************************************
* Static data internal to this module.
**********************************************************************/

// we keep a linked list of header_info's describing each image as told to us by dyld
static header_info *    FirstHeader = 0;

// Hash table of classes
static NXHashTable *            class_hash = 0;
static NXHashTablePrototype     classHashPrototype =
{
    (unsigned (*) (const void *, const void *))                 classHash,
    (int (*)(const void *, const void *, const void *)) classIsEqual,
    NXNoEffectFree, 0
};

// Exported copy of class_hash variable (hook for debugging tools)
NXHashTable *_objc_debug_class_hash = NULL;

// Function pointer objc_getClass calls through when class is not found
static int                      (*objc_classHandler) (const char *) = _objc_defaultClassHandler;

// Function pointer called by objc_getClass and objc_lookupClass when 
// class is not found. _objc_classLoader is called before objc_classHandler.
static BOOL (*_objc_classLoader)(const char *) = NULL;

// Category and class registries
static NXMapTable *             category_hash = NULL;


static int Postpone_install_relationships = 0;

static NXMapTable *             pendingClassRefsMap = 0;

/***********************************************************************
* objc_dump_class_hash.  Log names of all known classes.
**********************************************************************/
void    objc_dump_class_hash           (void)
{
    NXHashTable *       table;
    unsigned            count;
    struct objc_class   *               data;
    NXHashState         state;

    table = class_hash;
    count = 0;
    state = NXInitHashState (table);
    while (NXNextHashState (table, &state, (void **) &data))
        printf ("class %d: %s\n", ++count, data->name);
}

/***********************************************************************
* classHash.
**********************************************************************/
static unsigned         classHash              (void *          info,
                                   struct objc_class *          data)
{
    // Nil classes hash to zero
    if (!data)
        return 0;

    // Call through to real hash function
    return _objc_strhash ((unsigned char *) ((struct objc_class *) data)->name);
}

/***********************************************************************
* classIsEqual.  Returns whether the class names match.  If we ever
* check more than the name, routines like objc_lookUpClass have to
* change as well.
**********************************************************************/
static int              classIsEqual           (void *          info,
                                 struct objc_class *            name,
                                 struct objc_class *            cls)
{
    // Standard string comparison
    // Our local inlined version is significantly shorter on PPC and avoids the
    // mflr/mtlr and dyld_stub overhead when calling strcmp.
    return _objc_strcmp(name->name, cls->name) == 0;
}

/***********************************************************************
* _objc_init_class_hash.  Return the class lookup table, create it if
* necessary.
**********************************************************************/
void    _objc_init_class_hash          (void)
{
    // Do nothing if class hash table already exists
    if (class_hash)
        return;

    // Provide a generous initial capacity to cut down on rehashes
    // at launch time.  A smallish Foundation+AppKit program will have
    // about 520 classes.  Larger apps (like IB or WOB) have more like
    // 800 classes.  Some customers have massive quantities of classes.
    // Foundation-only programs aren't likely to notice the ~6K loss.
    class_hash = NXCreateHashTableFromZone (classHashPrototype,
                                            1024,
                                            nil,
                                            _objc_create_zone ());
    _objc_debug_class_hash = class_hash;
}

/***********************************************************************
* objc_getClassList.  Return the known classes.
**********************************************************************/
int objc_getClassList(Class *buffer, int bufferLen) {
    NXHashState state;
    struct objc_class * class;
    int cnt, num;

    OBJC_LOCK(&classLock);
    num = NXCountHashTable(class_hash);
    if (NULL == buffer) {
        OBJC_UNLOCK(&classLock);
        return num;
    }
    cnt = 0;
    state = NXInitHashState(class_hash);
    while (cnt < bufferLen  &&  
           NXNextHashState(class_hash, &state, (void **)&class)) 
    {
        buffer[cnt++] = class;
    }
    OBJC_UNLOCK(&classLock);
    return num;
}

/***********************************************************************
* objc_getClasses.  Return class lookup table.
*
* NOTE: This function is very dangerous, since you cannot safely use
* the hashtable without locking it, and the lock is private!
**********************************************************************/
void *          objc_getClasses        (void)
{
    // Return the class lookup hash table
    return class_hash;
}

/***********************************************************************
* _objc_defaultClassHandler.  Default objc_classHandler.  Does nothing.
**********************************************************************/
static int      _objc_defaultClassHandler      (const char *    clsName)
{
    // Return zero so objc_getClass doesn't bother re-searching
    return 0;
}

/***********************************************************************
* objc_setClassHandler.  Set objc_classHandler to the specified value.
*
* NOTE: This should probably deal with userSuppliedHandler being NULL,
* because the objc_classHandler caller does not check... it would bus
* error.  It would make sense to handle NULL by restoring the default
* handler.  Is anyone hacking with this, though?
**********************************************************************/
void    objc_setClassHandler    (int    (*userSuppliedHandler) (const char *))
{
    objc_classHandler = userSuppliedHandler;
}

/***********************************************************************
* objc_getClass.  Return the id of the named class.  If the class does
* not exist, call _objc_classLoader and then objc_classHandler, either of 
* which may create a new class.
* Warning: doesn't work if aClassName is the name of a posed-for class's isa!
**********************************************************************/
id              objc_getClass          (const char *    aClassName)
{
    struct objc_class   cls;
    id                                  ret;

    cls.name = aClassName;

    // Check the hash table
    OBJC_LOCK (&classLock);
    ret = (id) NXHashGet (class_hash, &cls);
    OBJC_UNLOCK (&classLock);

    // If not found, go call objc_classLoader and try again
    if (!ret  &&  _objc_classLoader  &&  (*_objc_classLoader)(aClassName))
    {
        OBJC_LOCK (&classLock);
        ret = (id) NXHashGet (class_hash, &cls);
        OBJC_UNLOCK (&classLock);
    }

    // If not found, go call objc_classHandler and try again
    if (!ret && (*objc_classHandler)(aClassName))
    {
        OBJC_LOCK (&classLock);
        ret = (id) NXHashGet (class_hash, &cls);
        OBJC_UNLOCK (&classLock);
    }

    return ret;
}

/***********************************************************************
* objc_lookUpClass.  Return the id of the named class.
* If the class does not exist, call _objc_classLoader, which may create 
* a new class.
*
* Formerly objc_getClassWithoutWarning ()
**********************************************************************/
id              objc_lookUpClass       (const char *    aClassName)
{
    struct objc_class   cls;
    id                                  ret;

    cls.name = aClassName;

    // Check the hash table
    OBJC_LOCK (&classLock);
    ret = (id) NXHashGet (class_hash, &cls);
    OBJC_UNLOCK (&classLock);

    // If not found, go call objc_classLoader and try again
    if (!ret  &&  _objc_classLoader  &&  (*_objc_classLoader)(aClassName))
    {
        OBJC_LOCK (&classLock);
        ret = (id) NXHashGet (class_hash, &cls);
        OBJC_UNLOCK (&classLock);
    }

    // Don't call objc_classHandler; it's only used by objc_getClass().

    return ret;
}

/***********************************************************************
* objc_getMetaClass.  Return the id of the meta class the named class.
* Warning: doesn't work if aClassName is the name of a posed-for class's isa!
**********************************************************************/
id              objc_getMetaClass       (const char *   aClassName)
{
    struct objc_class * cls;

    cls = objc_getClass (aClassName);
    if (!cls)
    {
        _objc_inform ("class `%s' not linked into application", aClassName);
        return Nil;
    }

    return cls->isa;
}

/***********************************************************************
* objc_addClass.  Add the specified class to the table of known classes,
* after doing a little verification and fixup.
**********************************************************************/
void            objc_addClass           (Class          cls)
{
    // Synchronize access to hash table
    OBJC_LOCK (&classLock);

    // Make sure both the class and the metaclass have caches!
    // Clear all bits of the info fields except CLS_CLASS and CLS_META.
    // Normally these bits are already clear but if someone tries to cons
    // up their own class on the fly they might need to be cleared.
    if (((struct objc_class *)cls)->cache == NULL)
    {
        ((struct objc_class *)cls)->cache = (Cache) &emptyCache;
        ((struct objc_class *)cls)->info = CLS_CLASS;
    }

    if (((struct objc_class *)cls)->isa->cache == NULL)
    {
        ((struct objc_class *)cls)->isa->cache = (Cache) &emptyCache;
        ((struct objc_class *)cls)->isa->info = CLS_META;
    }

    // Add the class to the table
    (void) NXHashInsert (class_hash, cls);

    // Desynchronize
    OBJC_UNLOCK (&classLock);
}

/***********************************************************************
* _objcTweakMethodListPointerForClass.
**********************************************************************/
static void     _objcTweakMethodListPointerForClass     (struct objc_class *    cls)
{
    struct objc_method_list *   originalList;
    const int                                   initialEntries = 4;
    int                                                 mallocSize;
    struct objc_method_list **  ptr;

    // Remember existing list
    originalList = (struct objc_method_list *) cls->methodLists;

    // Allocate and zero a method list array
    mallocSize   = sizeof(struct objc_method_list *) * initialEntries;
    ptr      = (struct objc_method_list **) malloc_zone_calloc (_objc_create_zone (), 1, mallocSize);

    // Insert the existing list into the array
    ptr[initialEntries - 1] = END_OF_METHODS_LIST;
    ptr[0] = originalList;

    // Replace existing list with array
    ((struct objc_class *)cls)->methodLists = ptr;
    ((struct objc_class *)cls)->info |= CLS_METHOD_ARRAY;

    // Do the same thing to the meta-class
    if (((((struct objc_class *)cls)->info & CLS_CLASS) != 0) && cls->isa)
        _objcTweakMethodListPointerForClass (cls->isa);
}

/***********************************************************************
* _objc_insertMethods.
**********************************************************************/
void    _objc_insertMethods    (struct objc_method_list *       mlist,
                             struct objc_method_list ***        list)
{
    struct objc_method_list **                  ptr;
    volatile struct objc_method_list ** tempList;
    int                                                                 endIndex;
    int                                                                 oldSize;
    int                                                                 newSize;

    // Locate unused entry for insertion point
    ptr = *list;
    while ((*ptr != 0) && (*ptr != END_OF_METHODS_LIST))
        ptr += 1;

    // If array is full, double it
    if (*ptr == END_OF_METHODS_LIST)
    {
        // Calculate old and new dimensions
        endIndex = ptr - *list;
        oldSize  = (endIndex + 1) * sizeof(void *);
        newSize  = oldSize + sizeof(struct objc_method_list *); // only increase by 1

        // Replace existing array with copy twice its size
        tempList = (struct objc_method_list **) malloc_zone_realloc ((void *) _objc_create_zone (),
                                                                     (void *) *list,
                                                                     (size_t) newSize);
        *list = tempList;

        // Zero out addition part of new array
        bzero (&((*list)[endIndex]), newSize - oldSize);

        // Place new end marker
        (*list)[(newSize/sizeof(void *)) - 1] = END_OF_METHODS_LIST;

        // Insertion point corresponds to old array end
        ptr = &((*list)[endIndex]);
    }

    // Right shift existing entries by one
    bcopy (*list, (*list) + 1, ((void *) ptr) - ((void *) *list));

    // Insert at method list at beginning of array
    **list = mlist;
}

/***********************************************************************
* _objc_removeMethods.
**********************************************************************/
void    _objc_removeMethods    (struct objc_method_list *       mlist,
                             struct objc_method_list ***        list)
{
    struct objc_method_list **  ptr;

    // Locate list in the array
    ptr = *list;
    while (*ptr != mlist) {
        // fix for radar # 2538790
        if ( *ptr == END_OF_METHODS_LIST ) return;
        ptr += 1;
    }

    // Remove this entry
    *ptr = 0;

    // Left shift the following entries
    while (*(++ptr) != END_OF_METHODS_LIST)
        *(ptr-1) = *ptr;
    *(ptr-1) = 0;
}

/***********************************************************************
* _objc_add_category.  Install the specified category's methods and
* protocols into the class it augments.
**********************************************************************/
static inline void _objc_add_category(struct objc_class *cls, struct objc_category *category, int version)
{
    // Augment instance methods
    if (category->instance_methods)
        _objc_insertMethods (category->instance_methods, &cls->methodLists);

    // Augment class methods
    if (category->class_methods)
        _objc_insertMethods (category->class_methods, &cls->isa->methodLists);

    // Augment protocols
    if ((version >= 5) && category->protocols)
    {
        if (cls->isa->version >= 5)
        {
            category->protocols->next = cls->protocols;
            cls->protocols                = category->protocols;
            cls->isa->protocols       = category->protocols;
        }
        else
        {
            _objc_inform ("unable to add protocols from category %s...\n", category->category_name);
            _objc_inform ("class `%s' must be recompiled\n", category->class_name);
        }
    }
}

/***********************************************************************
* _objc_add_category_flush_caches.  Install the specified category's methods into
* the class it augments, and flush the class' method cache.
*
**********************************************************************/
static void _objc_add_category_flush_caches(struct objc_class *cls, struct objc_category *category, int version)
{
    // Install the category's methods into its intended class
    _objc_add_category (cls, category, version);

    // Flush caches so category's methods can get called
    _objc_flush_caches (cls);
}

/***********************************************************************
* _objc_resolve_categories_for_class.  Install all categories intended
* for the specified class, in reverse order from the order in which we
* found the categories in the image.
* This is done as lazily as we can.
**********************************************************************/
void    _objc_resolve_categories_for_class  (struct objc_class *        cls)
{
    _objc_unresolved_category * cat;
    _objc_unresolved_category * next;

    // Nothing to do if there are no categories at all
    if (!category_hash)
        return;

    // Locate and remove first element in category list
    // associated with this class
    cat = NXMapRemove (category_hash, cls->name);

    // Traverse the list of categories, if any, registered for this class
    while (cat)
    {
        if (cat->bindme) {
            _objc_bindModuleContainingCategory(cat->cat);
        }
        // Install the category
        // use the non-flush-cache version since we are only
        // called from the class intialization code
        _objc_add_category (cls, cat->cat, cat->version);

        // Delink and reclaim this registration
        next = cat->next;
        free (cat);
        cat = next;
    }
}

/***********************************************************************
* _objc_register_category.  Add the specified category to the registry
* of categories to be installed later (once we know for sure which
                                       * classes we have).  If there are multiple categories on a given class,
* they will be processed in reverse order from the order in which they
* were found in the image.
**********************************************************************/
static void _objc_register_category    (struct objc_category *  cat,
                                        long                                    version,
                                        int                                             bindme)
{
    _objc_unresolved_category * new_cat;
    _objc_unresolved_category * old;
    struct objc_class *theClass;


    // If the category's class exists, just add the category
    // We could check to see if its initted, and if not, defer this
    // work until _objc_resolve_categories_for_class for all cases
    // The only trick then is whether we need to bind it.  This
    // might be doable if we store an obscured pointer so that we
    // avoid touching the memory... [BG 5/2001 still in think mode]
    if (theClass = objc_lookUpClass (cat->class_name))
    {
        if (bindme) {
            _objc_bindModuleContainingCategory(cat);
        }
        _objc_add_category_flush_caches (theClass, cat, version);
        return;
    }

    // Create category lookup table if needed
    if (!category_hash)
        category_hash = NXCreateMapTableFromZone (NXStrValueMapPrototype,
                                                  128,
                                                  _objc_create_zone ());

    // Locate an existing category, if any, for the class.  This is linked
    // after the new entry, so list is LIFO.
    old = NXMapGet (category_hash, cat->class_name);

    // Register the category to be fixed up later
    new_cat = malloc_zone_malloc (_objc_create_zone (),
                                  sizeof(_objc_unresolved_category));
    new_cat->next    = old;
    new_cat->cat     = cat;
    new_cat->version = version;
    new_cat->bindme  = bindme;                  // could use a bit in the next pointer instead of a whole word
    (void) NXMapInsert (category_hash, cat->class_name , new_cat);
}

/***********************************************************************
* _objc_add_categories_from_image.
**********************************************************************/
static void _objc_add_categories_from_image (header_info *  hi)
{
    Module              mods;
    unsigned int        midx;
    int                 isDynamic = (hi->mhdr->filetype == MH_DYLIB) || (hi->mhdr->filetype == MH_BUNDLE);

    if (_objcHeaderIsReplacement(hi)) {
        // Ignore any categories in this image
        return;
    }

    // Major loop - process all modules in the header
    mods = (Module) ((unsigned long) hi->mod_ptr + hi->image_slide);

    trace(0xb120, hi->mod_count, 0, 0);

    for (midx = 0; midx < hi->mod_count; midx += 1)
    {
        unsigned int    index;
        unsigned int    total;

        // Nothing to do for a module without a symbol table
        if (mods[midx].symtab == NULL)
            continue;

        // Total entries in symbol table (class entries followed
        // by category entries)
        total = mods[midx].symtab->cls_def_cnt +
            mods[midx].symtab->cat_def_cnt;


        trace(0xb123, midx, mods[midx].symtab->cat_def_cnt, 0);

        // Minor loop - register all categories from given module
        for (index = mods[midx].symtab->cls_def_cnt; index < total; index += 1)
        {
            _objc_register_category(mods[midx].symtab->defs[index], mods[midx].version, isDynamic && !all_modules_prebound);
        }

        trace(0xb124, midx, 0, 0);
    }

    trace(0xb12f, 0, 0, 0);
}


/***********************************************************************
* _headerForAddress.
* addr can be a class or a category
**********************************************************************/
static const header_info *_headerForAddress(void *addr)
{
    const struct segment_command *      objcSeg;
    unsigned int                        size;
    unsigned long                       vmaddrPlus;
    header_info *               hInfo;

    // Check all headers in the vector
    for (hInfo = FirstHeader; hInfo != NULL; hInfo = hInfo->next)
    {
        // Locate header data, if any
        objcSeg = (struct segment_command *)hInfo->objcData;
        size = hInfo->objcDataSize;
        if (!objcSeg)
            continue;

        // Is the class in this header?
        vmaddrPlus = (unsigned long) objcSeg->vmaddr + hInfo->image_slide;
        if ((vmaddrPlus <= (unsigned long) addr) &&
            ((unsigned long) addr < (vmaddrPlus + size)))
            return hInfo;
    }

    // Not found
    return 0;
}


/***********************************************************************
* _headerForCategory
* Return the image header containing this category, or NULL
**********************************************************************/
static const header_info *_headerForCategory(struct objc_category *cat)
{
    return _headerForAddress(cat);
}


/***********************************************************************
* _headerForClass
* Return the image header containing this class, or NULL.
* Returns NULL on runtime-constructed classes, and the NSCF classes.
**********************************************************************/
static const header_info *_headerForClass(struct objc_class *cls)
{
    return _headerForAddress(cls);
}


/***********************************************************************
* _moduleForClassFromImage
* Returns the module containing the definition for a class, or NULL.
* The class is assumed to be in the given image, and the module
* returned will be in that image.
**********************************************************************/
static Module _moduleForClassFromImage(struct objc_class *cls,
                                       const header_info *hInfo)
{
    Module mods = (Module)((unsigned long)hInfo->mod_ptr + hInfo->image_slide);
    int m, d;
    for (m = 0; m < hInfo->mod_count; m++) {
        if (mods[m].symtab) {
            for (d = 0; d < mods[m].symtab->cls_def_cnt; d++) {
                if (cls == (struct objc_class *) mods[m].symtab->defs[d]) {
                    return &mods[m];
                }
            }
        }
    }
    return NULL;
}


/***********************************************************************
* _moduleForCategoryFromImage
* Returns the module containing the definition for a category, or NULL.
* The category is assumed to be in the given image, and the module
* returned will be in that image.
**********************************************************************/
static Module _moduleForCategoryFromImage(struct objc_category *cat,
                                          const header_info *hInfo)
{
    Module mods = (Module)((unsigned long)hInfo->mod_ptr + hInfo->image_slide);
    int m, d;
    for (m = 0; m < hInfo->mod_count; m++) {
        if (mods[m].symtab) {
            for (d = mods[m].symtab->cls_def_cnt;
                 d < mods[m].symtab->cls_def_cnt + mods[m].symtab->cat_def_cnt;
                 d++)
            {
                if (cat == (struct objc_category *) mods[m].symtab->defs[d]) {
                    return &mods[m];
                }
            }
        }
    }
    return NULL;
}


/***********************************************************************
* _nameForHeader.
**********************************************************************/
const char *    _nameForHeader         (const headerType *      header)
{
    return _getObjcHeaderName ((headerType *) header);
}

/***********************************************************************
* checkForPendingClassReferences.  Complete any fixups registered for
* this class.
**********************************************************************/
static void     _objc_checkForPendingClassReferences           (struct objc_class *     cls)
{
    PendingClass *      pending;

    // Nothing to do if there are no pending classes
    if (!pendingClassRefsMap)
        return;

    // Get pending list for this class
    pending = NXMapGet (pendingClassRefsMap, cls->name);
    if (!pending)
        return;

    // Remove the list from the table
    (void) NXMapRemove (pendingClassRefsMap, cls->name);

    // Process all elements in the list
    while (pending)
    {
        PendingClass *  next;

        // Remember follower for loop
        next = pending->next;

        // Fill in a pointer to Class
        // (satisfies caller of objc_pendClassReference)
        if (pending->ref)
            *pending->ref = objc_getClass (cls->name);

        // Fill in super, isa, cache, and version for the class
        // and its meta-class
        // (satisfies caller of objc_pendClassInstallation)
        // NOTE: There must be no more than one of these for
        // any given classToSetUp
        if (pending->classToSetUp)
        {
            struct objc_class * fixCls;

            // Locate the Class to be fixed up
            fixCls = pending->classToSetUp;

            // Set up super class fields with names to be replaced by pointers
            fixCls->super_class      = (struct objc_class *) pending->nameof_superclass;
            fixCls->isa->super_class = (struct objc_class *) pending->nameof_superclass;

            // Fix up class pointers, version, and cache pointers
            _class_install_relationships (fixCls, pending->version);
        }

        // Reclaim the element
        free (pending);

        // Move on
        pending = next;
    }
}

/***********************************************************************
* newPending.  Allocate and zero a PendingClass structure.
**********************************************************************/
static inline PendingClass *    newPending             (void)
{
    PendingClass *      pending;

    pending = (PendingClass *) malloc_zone_calloc (_objc_create_zone (), 1, sizeof(PendingClass));

    return pending;
}

/***********************************************************************
* pendingClassRefsMapTable.  Return a pointer to the lookup table for
* pending classes.
**********************************************************************/
static inline NXMapTable *      pendingClassRefsMapTable    (void)
{
    // Allocate table if needed
    if (!pendingClassRefsMap)
        pendingClassRefsMap = NXCreateMapTableFromZone (NXStrValueMapPrototype, 10, _objc_create_zone ());

    // Return table pointer
    return pendingClassRefsMap;
}

/***********************************************************************
* objc_pendClassReference.  Register the specified class pointer (ref)
* to be filled in later with a pointer to the class having the specified
* name.
**********************************************************************/
void    objc_pendClassReference        (const char *    className,
                                     struct objc_class * *              ref)
{
    NXMapTable *                table;
    PendingClass *              pending;

    // Create and/or locate pending class lookup table
    table = pendingClassRefsMapTable ();

    // Create entry containing the class reference
    pending = newPending ();
    pending->ref = ref;

    // Link new entry into head of list of entries for this class
    pending->next = NXMapGet (pendingClassRefsMap, className);

    // (Re)place entry list in the table
    (void) NXMapInsert (table, className, pending);
}

/***********************************************************************
* objc_pendClassInstallation.  Register the specified class to have its
* super class pointers filled in later because the superclass is not
* yet found.
**********************************************************************/
void    objc_pendClassInstallation     (struct objc_class *cls, int version)
{
    NXMapTable *                table;
    PendingClass *              pending;

    // Create and/or locate pending class lookup table
    table = pendingClassRefsMapTable ();

    // Create entry referring to this class
    pending = newPending ();
    pending->classToSetUp          = cls;
    pending->nameof_superclass = (const char *) cls->super_class;
    pending->version       = version;

    // Link new entry into head of list of entries for this class
    pending->next                  = NXMapGet (pendingClassRefsMap, cls->super_class);

    // (Re)place entry list in the table
    (void) NXMapInsert (table, cls->super_class, pending);
}

/***********************************************************************
* _objc_add_classes_from_image.  Install all classes contained in the
* specified image.
**********************************************************************/
static void     _objc_add_classes_from_image(NXHashTable *clsHash, header_info *hi)
{
    unsigned int        index;
    unsigned int        midx;
    Module              mods;
    int                 isDynamic = (hi->mhdr->filetype == MH_DYLIB) || (hi->mhdr->filetype == MH_BUNDLE);

    if (_objcHeaderIsReplacement(hi)) {
        // Ignore any classes in this image
        return;
    }

    // Major loop - process all modules in the image
    mods = (Module) ((unsigned long) hi->mod_ptr + hi->image_slide);
    for (midx = 0; midx < hi->mod_count; midx += 1)
    {
        // Skip module containing no classes
        if (mods[midx].symtab == NULL)
            continue;

        // Minor loop - process all the classes in given module
        for (index = 0; index < mods[midx].symtab->cls_def_cnt; index += 1)
        {
            struct objc_class * oldCls;
            struct objc_class * newCls;

            // Locate the class description pointer
            newCls = mods[midx].symtab->defs[index];

            // remember to bind the module on initialization
            if (isDynamic  &&  !all_modules_prebound)
                newCls->info |= CLS_NEED_BIND ;

            // Convert old style method list to the new style
            _objcTweakMethodListPointerForClass (newCls);

            oldCls = NXHashInsert (clsHash, newCls);

            // Non-Nil oldCls is a class that NXHashInsert just
            // bumped from table because it has the same name
            // as newCls
            if (oldCls)
            {
                const header_info *     oldHeader;
                const header_info *     newHeader;
                const char *            oldName;
                const char *            newName;

                // Log the duplication
                oldHeader = _headerForClass (oldCls);
                newHeader = _headerForClass (newCls);
                oldName   = _nameForHeader  (oldHeader->mhdr);
                newName   = _nameForHeader  (newHeader->mhdr);
                _objc_inform ("Both %s and %s have implementations of class %s.",
                              oldName, newName, oldCls->name);
                _objc_inform ("Using implementation from %s.", newName);

                // Use the chosen class
                // NOTE: Isn't this a NOP?
                newCls = objc_lookUpClass (oldCls->name);
            }

            // Unless newCls was a duplicate, and we chose the
            // existing one instead, set the version in the meta-class
            if (newCls != oldCls)
                newCls->isa->version = mods[midx].version;

            // Install new categories intended for this class
            // NOTE: But, if we displaced an existing "isEqual"
            // class, the categories have already been installed
            // on an old class and are gone from the registry!!

            // we defer this work until the class is initialized.
            //_objc_resolve_categories_for_class (newCls);

            // Resolve (a) pointers to the named class, and/or
            // (b) the super_class, cache, and version
            // fields of newCls and its meta-class
            // NOTE: But, if we displaced an existing "isEqual"
            // class, this has already been done... with an
            // old-now-"unused" class!!
            _objc_checkForPendingClassReferences (newCls);

        }
    }
}

/***********************************************************************
* _objc_fixup_string_objects_for_image.  Initialize the isa pointers
* of all NSConstantString objects.
**********************************************************************/
static void     _objc_fixup_string_objects_for_image   (header_info *   hi)
{
    unsigned int                                size;
    OBJC_CONSTANT_STRING_PTR    section;
    struct objc_class *                                         constantStringClass;
    unsigned int                                index;

    // Locate section holding string objects
    section = _getObjcStringObjects ((headerType *) hi->mhdr, &size);
    if (!section || !size)
        return;
    section = (OBJC_CONSTANT_STRING_PTR) ((unsigned long) section + hi->image_slide);

    // Luckily NXConstantString is the same size as NSConstantString
    constantStringClass = objc_getClass ("NSConstantString");

    // Process each string object in the section
    for (index = 0; index < size; index += 1)
    {
        struct objc_class * *           isaptr;

        isaptr = (struct objc_class * *) OBJC_CONSTANT_STRING_DEREF section[index];
        if (*isaptr == 0)
            *isaptr = constantStringClass;
    }
}

/***********************************************************************
* _objc_map_class_refs_for_image.  Convert the class ref entries from
* a class name string pointer to a class pointer.  If the class does
* not yet exist, the reference is added to a list of pending references
* to be fixed up at a later date.
**********************************************************************/
static void _objc_map_class_refs_for_image (header_info * hi)
{
    struct objc_class * *                       cls_refs;
    unsigned int        size;
    unsigned int        index;

    // Locate class refs in image
    cls_refs = _getObjcClassRefs ((headerType *) hi->mhdr, &size);
    if (!cls_refs)
        return;
    cls_refs = (struct objc_class * *) ((unsigned long) cls_refs + hi->image_slide);

    // Process each class ref
    for (index = 0; index < size; index += 1)
    {
        const char *    ref;
        struct objc_class *             cls;

        // Get ref to convert from name string to class pointer
        ref = (const char *) cls_refs[index];

        // Get pointer to class of this name
        cls = (struct objc_class *)objc_lookUpClass (ref);

        // If class isn't there yet, use pending mechanism
        if (!cls)
        {
            // Register this ref to be set later
            objc_pendClassReference (ref, &cls_refs[index]);

            // Use place-holder class
            cls_refs[index] = _objc_getNonexistentClass ();
        }

        // Replace name string pointer with class pointer
        else
            cls_refs[index] = cls;
    }
}

/***********************************************************************
* map_selrefs.  Register each selector in the specified array.  If a
* given selector is already registered, update this array to point to
* the registered selector string.
**********************************************************************/
static inline void map_selrefs(SEL *sels, unsigned int  cnt)
{
    unsigned int        index;

    sel_lock();

    // Process each selector
    for (index = 0; index < cnt; index += 1)
    {
        SEL     sel;

        // Lookup pointer to uniqued string
        sel = sel_registerNameNoCopyNoLock ((const char *) sels[index]);

        // Replace this selector with uniqued one (avoid
        // modifying the VM page if this would be a NOP)
        if (sels[index] != sel)
            sels[index] = sel;
    }
    
    sel_unlock();
}


/***********************************************************************
* map_method_descs.  For each method in the specified method list,
* replace the name pointer with a uniqued selector.
**********************************************************************/
static void  map_method_descs (struct objc_method_description_list * methods)
{
    unsigned int        index;

    sel_lock();

    // Process each method
    for (index = 0; index < methods->count; index += 1)
    {
        struct objc_method_description *        method;
        SEL                                     sel;

        // Get method entry to fix up
        method = &methods->list[index];

        // Lookup pointer to uniqued string
        sel = sel_registerNameNoCopyNoLock ((const char *) method->name);

        // Replace this selector with uniqued one (avoid
        // modifying the VM page if this would be a NOP)
        if (method->name != sel)
            method->name = sel;
    }

    sel_unlock();
}

/***********************************************************************
* _fixup.
**********************************************************************/
@interface Protocol(RuntimePrivate)
+ _fixup: (OBJC_PROTOCOL_PTR)protos numElements: (int) nentries;
@end

/***********************************************************************
* _objc_fixup_protocol_objects_for_image.  For each protocol in the
* specified image, selectorize the method names and call +_fixup.
**********************************************************************/
static void _objc_fixup_protocol_objects_for_image (header_info * hi)
{
    unsigned int        size;
    OBJC_PROTOCOL_PTR   protos;
    unsigned int        index;

    // Locate protocols in the image
    protos = (OBJC_PROTOCOL_PTR) _getObjcProtocols ((headerType *) hi->mhdr, &size);
    if (!protos)
        return;

    // Apply the slide bias
    protos = (OBJC_PROTOCOL_PTR) ((unsigned long) protos + hi->image_slide);

    // Process each protocol
    for (index = 0; index < size; index += 1)
    {
        // Selectorize the instance methods
        if (protos[index] OBJC_PROTOCOL_DEREF instance_methods)
            map_method_descs (protos[index] OBJC_PROTOCOL_DEREF instance_methods);

        // Selectorize the class methods
        if (protos[index] OBJC_PROTOCOL_DEREF class_methods)
            map_method_descs (protos[index] OBJC_PROTOCOL_DEREF class_methods);
    }

    // Invoke Protocol class method to fix up the protocol
    [Protocol _fixup:(OBJC_PROTOCOL_PTR)protos numElements:size];
}

/***********************************************************************
* _objc_headerStart.  Return what headers we know about.
**********************************************************************/
header_info *   _objc_headerStart ()
{

    // Take advatage of our previous work
    return FirstHeader;
}

void _objc_bindModuleContainingList() {
    /* We define this for backwards binary compat with things which should not
    * have been using it (cough OmniWeb), but now it does nothing for them.
    */
}

/**********************************************************************
* _objc_bind_symbol.  Bind the module containing the symbol.  Use 2-level namespace API
*    Only look in images that we know to have ObjC symbols (e.g. 9 for Mail 7/2001)
*    Radar 2701686
***********************************************************************/
static void _objc_bind_symbol(const char *name)
{
    static header_info *lastHeader = NULL;
    header_info *hInfo;
    const headerType    *imageHeader = lastHeader ? lastHeader->mhdr : NULL;

    // First assume there is some locality and search where we last found a symbol
    if ( imageHeader
        && NSIsSymbolNameDefinedInImage(imageHeader, name)
        && NSLookupSymbolInImage(imageHeader, name, NSLOOKUPSYMBOLINIMAGE_OPTION_BIND) != NULL )
    {
        // Found
        return;
    }

    // Symbol wasn't found in the image we last searched
    // Search in all the images known to contain ObjcC
    for ( hInfo = FirstHeader; hInfo != NULL; hInfo = hInfo->next)
    {
        if (_objcHeaderIsReplacement(hInfo)) {
            continue; // no classes or categories used from image; skip it
        }
        imageHeader = hInfo->mhdr;
        if ( hInfo != lastHeader
             && NSIsSymbolNameDefinedInImage(imageHeader, name)
             && NSLookupSymbolInImage(imageHeader, name, NSLOOKUPSYMBOLINIMAGE_OPTION_BIND) != NULL )
        {
            // found
            lastHeader = hInfo;
            return;
        }
    }
    // die now, or later ??
    // _objc_fatal("could not find %s", name);
}

/***********************************************************************
* _symbolNameForCategory
* Constructs the symbol name for the given category.
* The symbol name is ".objc_category_name_<classname>_<categoryname>",
* where <classname> is the class name with the leading '%'s stripped.
* The caller must free() the result.
**********************************************************************/
static char *_symbolNameForCategory(Category cat)
{
    char *              class_name;
    char *              category_name;
    char *              name;

    class_name    = cat->class_name;
    category_name = cat->category_name;

    name = malloc(strlen(class_name) + strlen(category_name) + 30);

    while (*class_name == '%')
        class_name += 1;
    strcpy (name, ".objc_category_name_");
    strcat (name, class_name);
    strcat (name, "_");
    strcat (name, category_name);
    return name;
}

/***********************************************************************
* _symbolNameForClass
* Constructs the symbol name for the given class.
* The symbol name is ".objc_class_name_<classname>",
* where <classname> is the class name with the leading '%'s stripped.
* The caller must free() the result.
**********************************************************************/
static char *_symbolNameForClass(Class cls) 
{
    char *              name;
    const char *        class_name;

    class_name = cls->name;

    name = malloc(strlen(class_name) + 20);

    while (*class_name == '%')
        class_name += 1;
    strcpy (name, ".objc_class_name_");
    strcat (name, class_name);
    return name;
}


/***********************************************************************
* _objc_bindClassIfNeeded.
* If the given class is still marked as needs-bind, bind the module 
*   containing it.
* Called during _objc_call_loads_for_image just before sending +load, 
*   and during class_initialize just before sending +initialize.
**********************************************************************/
void _objc_bindClassIfNeeded(struct objc_class *cls)
{
    // Clear NEED_BIND *after* binding to prevent race
    // This assumes that simultaneous binding of one module by two threads is ok.
    if (cls->info & CLS_NEED_BIND) {
        _objc_bindModuleContainingClass(cls);
        cls->info &= ~CLS_NEED_BIND;
    }
}


/***********************************************************************
* _objc_bindModuleContainingCategory.  Bind the module containing the
* category. If that module is already bound, do nothing.
**********************************************************************/
static void _objc_bindModuleContainingCategory(struct objc_category *cat)
{
    const header_info *hInfo;
    
    if (PrintBinding) {
        _objc_inform("binding category %s(%s)",
                     cat->class_name, cat->category_name);
    }
    
    hInfo = _headerForCategory(cat);
    if (hInfo) {
        Module module = _moduleForCategoryFromImage(cat, hInfo);
        if (module) {
            _dyld_bind_objc_module(module);
            return;
        }
    }
    
    {
        // Header-finding or module-finding shortcut didn't work.
        // Bind using symbol name.
        char *symbolName = _symbolNameForCategory(cat);
        _objc_bind_symbol(symbolName);
        free(symbolName);
    }
}

    
/***********************************************************************
* _objc_bindModuleContainingClass.  Bind the module containing the
* class. If that module is already bound, do nothing.
* This is done lazily, just before calling +load or +initialize.
**********************************************************************/
void _objc_bindModuleContainingClass(struct objc_class *cls)
{
    const header_info *hInfo;
    
    if (PrintBinding) {
        _objc_inform("binding class %s", cls->name);
    }
    
    // Use the real class behind the poser
    if (CLS_GETINFO (cls, CLS_POSING)) {
        cls = getOriginalClassForPosingClass (cls);
    }
    
    hInfo = _headerForClass(cls);
    if (hInfo) {
        Module module = _moduleForClassFromImage(cls, hInfo);
        if (module) {
            _dyld_bind_objc_module(module);
            return;
        }
    }
    
    {
        // Module not bound, and header-finding or module-finding shortcut
        // didn't work. Bind using symbol name.
        // This happens for the NSCF class structs which are copied elsewhere.
        char *symbolName = _symbolNameForClass(cls);
        _objc_bind_symbol(symbolName);
        free(symbolName);
    }
}


/***********************************************************************
* _objc_addHeader.
*
**********************************************************************/

// tested with 2; typical case is 4, but OmniWeb & Mail push it towards 20
#define HINFO_SIZE 16

static int HeaderInfoCounter = 0;
static header_info HeaderInfoTable[HINFO_SIZE] = { {0} };

static header_info * _objc_addHeader(const headerType *header, unsigned long    vmaddr_slide)
{
    int mod_count;
    Module mod_ptr = _getObjcModules ((headerType *) header, &mod_count);
    char *image_info_ptr = (char *)_getObjcImageInfo((headerType *)header);
    header_info *result;
    
    // if there is no objc data - ignore this entry!
    if (mod_ptr == NULL) {
        return NULL;
    }

    if (HeaderInfoCounter < HINFO_SIZE) {
        // avoid mallocs for the common case
        result = &HeaderInfoTable[HeaderInfoCounter++];
    }
    else {
        result = malloc_zone_malloc(_objc_create_zone(), sizeof(header_info));
    }

    // Set up the new vector entry
    result->mhdr = header;
    result->mod_ptr = mod_ptr;
    result->mod_count  = mod_count;
    result->image_slide = vmaddr_slide;
    result->objcData = _getObjcHeaderData(header, &result->objcDataSize);
    if (image_info_ptr) {
        result->info = (objc_image_info *)(vmaddr_slide + image_info_ptr);
    } else {
        result->info = NULL;
    }

    // chain it on
    // (a simple lock here would go a long way towards thread safety)
    result->next = FirstHeader;
    FirstHeader = result;
    
    return result;
}

/**********************************************************************
* _objc_fatalHeader
*
* If we have it we're in trouble
**************************************************************************/
static void     _objc_fatalHeader(const headerType *header)
{
    header_info *hInfo;
    
    for (hInfo = FirstHeader; hInfo != NULL; hInfo = hInfo->next) {
        if (hInfo->mhdr == header) {
            _objc_fatal("cannot unmap an image containing ObjC data");
        }
    }
}

/***********************************************************************
* _objc_fixup_selector_refs.  Register all of the selectors in each
* image, and fix them all up.
*
**********************************************************************/
static void _objc_fixup_selector_refs   (const header_info *    hi)
{
    unsigned int        size;
    Module              mods;
    SEL *               messages_refs;

    mods = (Module) ((unsigned long) hi->mod_ptr + hi->image_slide);

    // Fix up message refs
    messages_refs = (SEL *) _getObjcMessageRefs ((headerType *) hi->mhdr, &size);
    if (messages_refs)
    {
        messages_refs = (SEL *) ((unsigned long) messages_refs + hi->image_slide);
        map_selrefs (messages_refs, size);
    }
}


/***********************************************************************
* _objc_call_loads_for_image.
**********************************************************************/
static void _objc_call_loads_for_image (header_info * header)
{
    struct objc_class *         cls;
    struct objc_class * *       pClass;
    Category *                  pCategory;
    IMP                         load_method;
    unsigned int                nModules;
    unsigned int                nClasses;
    unsigned int                nCategories;
    struct objc_symtab *        symtab;
    struct objc_module *        module;

    if (_objcHeaderIsReplacement(header)) {
        return; // Don't call +load again
    }

    // Major loop - process all modules named in header
    module = (struct objc_module *) ((unsigned long) header->mod_ptr + header->image_slide);
    for (nModules = header->mod_count; nModules; nModules -= 1, module += 1)
    {
        symtab = module->symtab;
        if (symtab == NULL)
            continue;

        // Minor loop - call the +load from each class in the given module
        for (nClasses = symtab->cls_def_cnt, pClass = (Class *) symtab->defs;
             nClasses;
             nClasses -= 1, pClass += 1)
        {
            struct objc_method_list **mlistp;
            cls = (struct objc_class *)*pClass;
            mlistp = get_base_method_list(cls->isa);
            if (cls->isa->methodLists && mlistp)
            {
                // Look up the method manually (vs messaging the class) to bypass
                // +initialize and cache fill on class that is not even loaded yet
                load_method = class_lookupNamedMethodInMethodList (*mlistp, "load");
                if (load_method) {
                    _objc_bindClassIfNeeded(cls);
                    (*load_method) ((id) cls, @selector(load));
                }
            }
        }

        // Minor loop - call the +load from augmented class of
        // each category in the given module
        for (nCategories = symtab->cat_def_cnt,
             pCategory = (Category *) &symtab->defs[symtab->cls_def_cnt];
             nCategories;
             nCategories -= 1, pCategory += 1)
        {
            struct objc_method_list *   methods;

            methods = (*pCategory)->class_methods;
            if (methods)
            {
                load_method = class_lookupNamedMethodInMethodList (methods, "load");
                if (load_method) {
                    // Strictly speaking we shouldn't need (and don't want) to get the class here
                    // The side effect we're looking for is to load it if needed.
                    // Since category +loads are rare we could spend some cycles finding out
                    // if we have a "bindme" TBD and do it here, saving a class load.
                    // But chances are the +load will cause class initialization anyway
                    cls = objc_getClass ((*pCategory)->class_name);
                    // the class & all categories are now bound in
                    (*load_method) ((id) cls, @selector(load));
                }
            }
        }
    }
}

/***********************************************************************
* runtime configuration
**********************************************************************/
static void objc_setConfiguration() {
    if ( LaunchingDebug == -1 ) {
        // watch image loading and binding
        LaunchingDebug = getenv("LaunchingDebug") != NULL;
    }
    if ( PrintBinding == -1 ) {
        PrintBinding = getenv("OBJC_PRINT_BIND") != NULL;
    }
}
/***********************************************************************
* objc_setMultithreaded.
**********************************************************************/
void objc_setMultithreaded (BOOL flag)
{
    // Nothing here. Thread synchronization in the runtime is always active.
}



/***********************************************************************
* _objc_pthread_destroyspecific
* Destructor for objc's per-thread data.
* arg shouldn't be NULL, but we check anyway.
**********************************************************************/
extern void _destroyInitializingClassList(struct _objc_initializing_classes *list);
void _objc_pthread_destroyspecific(void *arg)
{
    _objc_pthread_data *data = (_objc_pthread_data *)arg;
    if (data != NULL) {
        _destroyInitializingClassList(data->initializingClasses);

        // add further cleanup here...

        free(data);
    }
}


/***********************************************************************
* _objcInit.
* Library initializer called by dyld & from crt0
**********************************************************************/

void _objcInit(void) {
    header_info *hInfo;
    static int _done = 0;
    extern void __CFInitialize(void);
    extern int ptrace(int, int, int, int);      // a system call visible to sc_trace

    /* Protect against multiple invocations, as all library
        * initializers should. */
    if (0 != _done) return;
    _done = 1;

    ptrace(0xb000, 0, 0, 0);
    trace(0xb000, 0, 0, 0);

    // make sure CF is initialized before we go further;
    // someday this can be removed, as it'll probably be automatic
    __CFInitialize();
    
    pthread_key_create(&_objc_pthread_key, _objc_pthread_destroyspecific);

    // Create the class lookup table
    _objc_init_class_hash ();

    trace(0xb001, 0, 0, 0);

    objc_setConfiguration();    // Get our configuration
    
    trace(0xb003, 0, 0, 0);

    // a pre-cheetah comment:
    // XXXXX BEFORE HERE *NO* PAGES ARE STOMPED ON;

    // Register our image mapping routine with dyld so it
    // gets invoked when an image is added.  This also invokes
    // the callback right now on any images already present.

    // The modules present in the application and the existing
    // mapped images are treated differently than a newly discovered
    // mapped image - we process all modules for classes before
    // trying to install_relationships (glue up their superclasses)
    // or trying to send them any +load methods.

    // So we tell the map_image dyld callback to not do this part...

    Postpone_install_relationships = 1;

    // register for unmapping first so we can't miss any during load attempts
    _dyld_register_func_for_remove_image (&_objc_unmap_image);

    // finally, register for images
    _dyld_register_func_for_add_image (&_objc_map_image);

    // a pre-cheetah comment:
    // XXXXX BEFORE HERE *ALL* PAGES ARE STOMPED ON

    Postpone_install_relationships  = 0;

    trace(0xb006, 0, 0, 0);
    
    // Install relations on classes that were found
    for (hInfo = FirstHeader; hInfo != NULL; hInfo = hInfo->next)
    {
        int                     nModules;
        int                     index;
        struct objc_module *    module;
        struct objc_class *     cls;

        module = (struct objc_module *) ((unsigned long) hInfo->mod_ptr + hInfo->image_slide);
        for (nModules = hInfo->mod_count; nModules; nModules--, module++)
        {
            if (module->symtab) {
                for (index = 0; index < module->symtab->cls_def_cnt; index++)
                {
                    cls = (struct objc_class *) module->symtab->defs[index];
                    _class_install_relationships (cls, module->version);
                }
            }
        }

        trace(0xb007, hInfo, hInfo->mod_count, 0);

    }

    trace(0xb008, 0, 0, 0);

    for (hInfo = FirstHeader; hInfo != NULL; hInfo = hInfo->next)
    {
        // Initialize the isa pointers of all NXConstantString objects
        (void)_objc_fixup_string_objects_for_image (hInfo);

        // Convert class refs from name pointers to ids
        (void)_objc_map_class_refs_for_image (hInfo);
    }

    trace(0xb00a, 0, 0, 0);

    // For each image selectorize the method names and +_fixup each of
    // protocols in the image
    for (hInfo = FirstHeader; hInfo != NULL; hInfo = hInfo->next)
        _objc_fixup_protocol_objects_for_image (hInfo);

    for (hInfo = FirstHeader; hInfo != NULL; hInfo = hInfo->next)
        _objc_call_loads_for_image (hInfo);
    
    ptrace(0xb00f, 0, 0, 0);    // end of __initialize_objc ObjC init
    trace(0xb00f, 0, 0, 0);     // end of __initialize_objc ObjC init
}


/***********************************************************************
* _objc_map_image.
**********************************************************************/
static void     _objc_map_image(headerType *mh, unsigned long   vmaddr_slide)
{
    static int dumpClasses = -1;
    header_info *hInfo;

    if ( dumpClasses == -1 ) {
        if ( getenv("OBJC_DUMP_CLASSES") ) dumpClasses = 1;
        else dumpClasses = 0;
    }

    trace(0xb100, 0, 0, 0);

    // Add this header to the chain
    hInfo = _objc_addHeader (mh, vmaddr_slide);

    if (!hInfo) return;
    
    if (LaunchingDebug) { 
        _objc_syslog("objc_map_image for %s%s\n", 
                     _nameForHeader(mh), 
                     _objcHeaderIsReplacement(hInfo) ? " (replacement)" : "");
    }

    trace(0xb101, 0, 0, 0);

#ifdef MACOSX_PANTHER
    // Check if all loaded libraries up to and including this one are prebound
    // SPI introduced in Panther (Mac OS X 10.3)
    all_modules_prebound = _dyld_all_twolevel_modules_prebound();
    if (PrintBinding) {
        static int warned = -1;
        if (warned != all_modules_prebound) {
            _objc_inform("objc: binding: all_modules_prebound is now %d", 
                         all_modules_prebound);
            warned = all_modules_prebound;
        }
    }
#endif

    // Register any categories and/or classes and/or selectors this image contains
    _objc_add_categories_from_image (hInfo);

    trace(0xb103, 0, 0, 0);

    _objc_add_classes_from_image (class_hash, hInfo);

    trace(0xb104, 0, 0, 0);

    _objc_fixup_selector_refs (hInfo);

    trace(0xb105, 0, 0, 0);

    // Log all known class names, if asked
    if ( dumpClasses )
    {
        printf ("classes...\n");
        objc_dump_class_hash ();
    }

    if (!Postpone_install_relationships)
    {
        int                     nModules;
        int                     index;
        struct objc_module *    module;

        // Major loop - process each module
        module = (struct objc_module *) ((unsigned long) hInfo->mod_ptr + hInfo->image_slide);

        trace(0xb106, hInfo->mod_count, 0, 0);

        for (nModules = hInfo->mod_count; nModules; nModules--, module++)
        {
            if (!module->symtab) continue;

            // Minor loop - process each class in a given module
            for (index = 0; index < module->symtab->cls_def_cnt; index += 1)
            {
                struct objc_class * cls;

                // Locate the class description
                cls = (struct objc_class *) module->symtab->defs[index];

                // If there is no superclass or the superclass can be found,
                // install this class, and invoke the expected callback
                if (!((struct objc_class *)cls)->super_class || objc_lookUpClass ((char *) ((struct objc_class *)cls)->super_class))
                {
                    _class_install_relationships (cls, module->version);
                    if (callbackFunction)
                        (*callbackFunction) (cls, 0);
                }
                else
                {
                    // Super class can not be found yet, arrange for this class to
                    // be filled in later
                    objc_pendClassInstallation (cls, module->version);
                    ((struct objc_class *)cls)->super_class      = _objc_getNonexistentClass ();
                    ((struct objc_class *)cls)->isa->super_class = _objc_getNonexistentClass ();
                }
            }
        }

        trace(0xb108, 0, 0, 0);

        // Initialize the isa pointers of all NXConstantString objects
        _objc_fixup_string_objects_for_image (hInfo);

        trace(0xb109, 0, 0, 0);

        // Convert class refs from name pointers to ids
        _objc_map_class_refs_for_image (hInfo);

        trace(0xb10a, 0, 0, 0);

        // Selectorize the method names and +_fixup each of
        // protocols in the image
        _objc_fixup_protocol_objects_for_image (hInfo);

        trace(0xb10b, 0, 0, 0);

        // Call +load on all classes and categorized classes
        _objc_call_loads_for_image (hInfo);

        trace(0xb10c, 0, 0, 0);
    }

    trace(0xb10f, 0, 0, 0);
}

/***********************************************************************
* _objc_unmap_image.
**********************************************************************/
static void     _objc_unmap_image(headerType *mh, unsigned long vmaddr_slide) {
    // we shouldn't have it if it didn't have objc data
    // if we do have it, do a fatal
    _objc_fatalHeader(mh);
}

/***********************************************************************
* _objc_setNilReceiver
**********************************************************************/
id _objc_setNilReceiver(id newNilReceiver)
{
    id oldNilReceiver;

    oldNilReceiver = _objc_nilReceiver;
    _objc_nilReceiver = newNilReceiver;

    return oldNilReceiver;
}

/***********************************************************************
* _objc_getNilReceiver
**********************************************************************/
id _objc_getNilReceiver(void)
{
    return _objc_nilReceiver;
}


/***********************************************************************
* _objc_setClassLoader
* Similar to objc_setClassHandler, but objc_classLoader is used for 
* both objc_getClass() and objc_lookupClass(), and objc_classLoader 
* pre-empts objc_classHandler. 
**********************************************************************/
void _objc_setClassLoader(BOOL (*newClassLoader)(const char *))
{
    _objc_classLoader = newClassLoader;
}