]> git.saurik.com Git - apple/dyld.git/blobdiff - src/dyldInitialization.cpp
dyld-635.2.tar.gz
[apple/dyld.git] / src / dyldInitialization.cpp
index a112d18389b88a0dcda1f7f034ebbd4d2b057302..e58d08e65f5d41066650a93ab112a2583685ce72 100644 (file)
 #include <stddef.h>
 #include <string.h>
 #include <stdlib.h>
+#include <Availability.h>
 #include <mach/mach.h>
 #include <mach-o/loader.h>
 #include <mach-o/ldsyms.h>
 #include <mach-o/reloc.h>
-#if __ppc__ || __ppc64__
-       #include <mach-o/ppc/reloc.h>
-#endif
 #if __x86_64__
        #include <mach-o/x86_64/reloc.h>
 #endif
 #include "dyld.h"
+#include "dyldSyscallInterface.h"
+
+// from dyld_gdb.cpp 
+extern void addImagesToAllImages(uint32_t infoCount, const dyld_image_info info[]);
+extern void syncProcessInfo();
 
 #ifndef MH_PIE
        #define MH_PIE 0x200000 
 #endif
 
+// currently dyld has no initializers, but if some come back, set this to non-zero
+#define DYLD_INITIALIZER_SUPPORT  0
 
 #if __LP64__
        #define LC_SEGMENT_COMMAND              LC_SEGMENT_64
        #define POINTER_RELOC GENERIC_RELOC_VANILLA
 #endif
 
-// from dyld.cpp
-namespace dyld { extern bool isRosetta(); };
+#ifndef BIND_OPCODE_THREADED
+#define BIND_OPCODE_THREADED    0xD0
+#endif
+
+#ifndef BIND_SUBOPCODE_THREADED_SET_BIND_ORDINAL_TABLE_SIZE_ULEB
+#define BIND_SUBOPCODE_THREADED_SET_BIND_ORDINAL_TABLE_SIZE_ULEB    0x00
+#endif
+
+#ifndef BIND_SUBOPCODE_THREADED_APPLY
+#define BIND_SUBOPCODE_THREADED_APPLY                                0x01
+#endif
+
+
+#if __has_feature(ptrauth_calls)
+#include <ptrauth.h>
+#endif
+
+
+#if TARGET_IPHONE_SIMULATOR
+const dyld::SyscallHelpers* gSyscallHelpers = NULL;
+#endif
 
 
 //
@@ -74,8 +98,14 @@ namespace dyld { extern bool isRosetta(); };
 namespace dyldbootstrap {
 
 
+
+#if DYLD_INITIALIZER_SUPPORT
+
 typedef void (*Initializer)(int argc, const char* argv[], const char* envp[], const char* apple[]);
 
+extern const Initializer  inits_start  __asm("section$start$__DATA$__mod_init_func");
+extern const Initializer  inits_end    __asm("section$end$__DATA$__mod_init_func");
+
 //
 // For a regular executable, the crt code calls dyld to run the executables initializers.
 // For a static executable, crt directly runs the initializers.
@@ -83,35 +113,72 @@ typedef void (*Initializer)(int argc, const char* argv[], const char* envp[], co
 // We pass argc, argv, etc in case libc.a uses those arguments
 //
 static void runDyldInitializers(const struct macho_header* mh, intptr_t slide, int argc, const char* argv[], const char* envp[], const char* apple[])
+{
+       for (const Initializer* p = &inits_start; p < &inits_end; ++p) {
+               (*p)(argc, argv, envp, apple);
+       }
+}
+#endif // DYLD_INITIALIZER_SUPPORT
+
+
+//
+//  The kernel may have slid a Position Independent Executable
+//
+static uintptr_t slideOfMainExecutable(const struct macho_header* mh)
 {
        const uint32_t cmd_count = mh->ncmds;
        const struct load_command* const cmds = (struct load_command*)(((char*)mh)+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) {
-                                               const uint8_t type = sect->flags & SECTION_TYPE;
-                                               if ( type == S_MOD_INIT_FUNC_POINTERS ){
-                                                       Initializer* inits = (Initializer*)(sect->addr + slide);
-                                                       const uint32_t count = sect->size / sizeof(uintptr_t);
-                                                       for (uint32_t i=0; i < count; ++i) {
-                                                               Initializer func = inits[i];
-                                                               func(argc, argv, envp, apple);
-                                                       }
-                                               }
-                                       }
-                               }
-                               break;
+               if ( cmd->cmd == LC_SEGMENT_COMMAND ) {
+                       const struct macho_segment_command* segCmd = (struct macho_segment_command*)cmd;
+                       if ( (segCmd->fileoff == 0) && (segCmd->filesize != 0)) {
+                               return (uintptr_t)mh - segCmd->vmaddr;
+                       }
                }
                cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
        }
+       return 0;
+}
+
+inline uint64_t read_uleb128(const uint8_t*& p, const uint8_t* end) {
+    uint64_t result = 0;
+    int         bit = 0;
+    do {
+        if (p == end)
+            throw "malformed uleb128 extends beyond trie";
+        uint64_t slice = *p & 0x7f;
+
+        if (bit >= 64 || slice << bit >> bit != slice)
+            throw "uleb128 too big for 64-bits";
+        else {
+            result |= (slice << bit);
+            bit += 7;
+        }
+    }
+    while (*p++ & 0x80);
+    return result;
 }
 
+inline int64_t read_sleb128(const uint8_t*& p, const uint8_t* end)
+{
+    int64_t result = 0;
+    int bit = 0;
+    uint8_t byte;
+    do {
+        if (p == end)
+            throw "malformed sleb128";
+        byte = *p++;
+        result |= (((int64_t)(byte & 0x7f)) << bit);
+        bit += 7;
+    } while (byte & 0x80);
+    // sign extend negative numbers
+    if ( (byte & 0x40) != 0 )
+        result |= (~0ULL) << bit;
+    return result;
+}
+
+
 //
 // If the kernel does not load dyld at its preferred address, we need to apply 
 // fixups to various initialized parts of the __DATA segment
@@ -123,7 +190,215 @@ static void rebaseDyld(const struct macho_header* mh, intptr_t slide)
        const uint32_t cmd_count = mh->ncmds;
        const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header));
        const struct load_command* cmd = cmds;
-       const struct macho_segment_command* linkEditSeg = NULL;
+
+    // First look for compressed info and use it if it exists.
+    const struct macho_segment_command* linkEditSeg = NULL;
+    const dyld_info_command* dyldInfoCmd = NULL;
+    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 ( strcmp(seg->segname, "__LINKEDIT") == 0 )
+                    linkEditSeg = seg;
+                break;
+            }
+            case LC_DYLD_INFO_ONLY:
+                dyldInfoCmd = (struct dyld_info_command*)cmd;
+                break;
+        }
+        if (dyldInfoCmd && linkEditSeg)
+            break;
+        cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
+    }
+    if ( linkEditSeg == NULL )
+        throw "dyld missing LINKEDIT";
+
+    // Reset the iterator.
+    cmd = cmds;
+
+    auto getSegmentAtIndex = [cmd_count, cmds](unsigned segIndex) -> const struct macho_segment_command* {
+        const struct load_command* cmd = cmds;
+        for (uint32_t i = 0; i < cmd_count; ++i) {
+            switch (cmd->cmd) {
+                case LC_SEGMENT_COMMAND:
+                    if (!segIndex) {
+                        const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
+                        return seg;
+                    }
+                    --segIndex;
+                    break;
+            }
+            cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
+        }
+        throw "out of bounds command";
+        return 0;
+    };
+
+    auto segActualLoadAddress = [&](unsigned segIndex) -> uintptr_t {
+        const struct macho_segment_command* seg = getSegmentAtIndex(segIndex);
+        return seg->vmaddr + slide;
+    };
+
+#if __has_feature(ptrauth_calls)
+    auto imageBaseAddress = [cmds, cmd_count]() -> uintptr_t {
+        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;
+                    if ( (seg->fileoff == 0) && (seg->filesize != 0) )
+                        return seg->vmaddr;
+                    break;
+                }
+            }
+            cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
+        }
+        return 0;
+    };
+#endif
+
+    if (dyldInfoCmd && (dyldInfoCmd->bind_size != 0) ) {
+        if ( dyldInfoCmd->rebase_size != 0 )
+            throw "unthreaded rebases are not supported";
+
+        const uint8_t* linkEditBase = (uint8_t*)(linkEditSeg->vmaddr + slide - linkEditSeg->fileoff);
+
+        const uint8_t* const start = linkEditBase + dyldInfoCmd->bind_off;
+        const uint8_t* const end = &start[dyldInfoCmd->bind_size];
+        const uint8_t* p = start;
+
+        uintptr_t segmentStartAddress = 0;
+        uint64_t segOffset = 0;
+        int segIndex = 0;
+#if __has_feature(ptrauth_calls)
+        uintptr_t fBaseAddress = imageBaseAddress();
+#endif
+        bool done = false;
+
+        while ( !done && (p < end) ) {
+            uint8_t immediate = *p & BIND_IMMEDIATE_MASK;
+            uint8_t opcode = *p & BIND_OPCODE_MASK;
+            ++p;
+            switch (opcode) {
+                case BIND_OPCODE_DONE:
+                    done = true;
+                    break;
+                case BIND_OPCODE_SET_DYLIB_ORDINAL_IMM:
+                    break;
+                case BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB:
+                    break;
+                case BIND_OPCODE_SET_DYLIB_SPECIAL_IMM:
+                    break;
+                case BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM:
+                    while (*p != '\0')
+                        ++p;
+                    ++p;
+                    break;
+                case BIND_OPCODE_SET_TYPE_IMM:
+                    break;
+                case BIND_OPCODE_SET_ADDEND_SLEB:
+                    read_sleb128(p, end);
+                    break;
+                case BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB:
+                    segIndex = immediate;
+                    segmentStartAddress = segActualLoadAddress(segIndex);
+                    segOffset = read_uleb128(p, end);
+                    break;
+                case BIND_OPCODE_ADD_ADDR_ULEB:
+                    segOffset += read_uleb128(p, end);
+                    break;
+                case BIND_OPCODE_DO_BIND:
+                    break;
+                case BIND_OPCODE_DO_BIND_ADD_ADDR_ULEB:
+                    break;
+                case BIND_OPCODE_DO_BIND_ADD_ADDR_IMM_SCALED:
+                    break;
+                case BIND_OPCODE_DO_BIND_ULEB_TIMES_SKIPPING_ULEB:
+                    read_uleb128(p, end);
+                    read_uleb128(p, end);
+                    break;
+                case BIND_OPCODE_THREADED:
+                    // Note the immediate is a sub opcode
+                    switch (immediate) {
+                        case BIND_SUBOPCODE_THREADED_SET_BIND_ORDINAL_TABLE_SIZE_ULEB:
+                            read_uleb128(p, end);
+                            break;
+                        case BIND_SUBOPCODE_THREADED_APPLY: {
+                            uint64_t delta = 0;
+                            do {
+                                uintptr_t address = segmentStartAddress + (uintptr_t)segOffset;
+                                uint64_t value = *(uint64_t*)address;
+
+#if __has_feature(ptrauth_calls)
+                                uint16_t diversity = (uint16_t)(value >> 32);
+                                bool hasAddressDiversity = (value & (1ULL << 48)) != 0;
+                                ptrauth_key key = (ptrauth_key)((value >> 49) & 0x3);
+                                bool isAuthenticated = (value & (1ULL << 63)) != 0;
+#endif
+                                bool isRebase = (value & (1ULL << 62)) == 0;
+                                if (isRebase) {
+
+#if __has_feature(ptrauth_calls)
+                                    if (isAuthenticated) {
+                                        // The new value for a rebase is the low 32-bits of the threaded value plus the slide.
+                                        uint64_t newValue = (value & 0xFFFFFFFF) + slide;
+                                        // Add in the offset from the mach_header
+                                        newValue += fBaseAddress;
+                                        // We have bits to merge in to the discriminator
+                                        uintptr_t discriminator = diversity;
+                                        if (hasAddressDiversity) {
+                                            // First calculate a new discriminator using the address of where we are trying to store the value
+                                            discriminator = __builtin_ptrauth_blend_discriminator((void*)address, discriminator);
+                                        }
+                                        switch (key) {
+                                            case ptrauth_key_asia:
+                                                newValue = (uintptr_t)__builtin_ptrauth_sign_unauthenticated((void*)newValue, ptrauth_key_asia, discriminator);
+                                                break;
+                                            case ptrauth_key_asib:
+                                                newValue = (uintptr_t)__builtin_ptrauth_sign_unauthenticated((void*)newValue, ptrauth_key_asib, discriminator);
+                                                break;
+                                            case ptrauth_key_asda:
+                                                newValue = (uintptr_t)__builtin_ptrauth_sign_unauthenticated((void*)newValue, ptrauth_key_asda, discriminator);
+                                                break;
+                                            case ptrauth_key_asdb:
+                                                newValue = (uintptr_t)__builtin_ptrauth_sign_unauthenticated((void*)newValue, ptrauth_key_asdb, discriminator);
+                                                break;
+                                        }
+                                        *(uint64_t*)address = newValue;
+                                    } else
+#endif
+                                    {
+                                        // Regular pointer which needs to fit in 51-bits of value.
+                                        // C++ RTTI uses the top bit, so we'll allow the whole top-byte
+                                        // and the signed-extended bottom 43-bits to be fit in to 51-bits.
+                                        uint64_t top8Bits = value & 0x0007F80000000000ULL;
+                                        uint64_t bottom43Bits = value & 0x000007FFFFFFFFFFULL;
+                                        uint64_t targetValue = ( top8Bits << 13 ) | (((intptr_t)(bottom43Bits << 21) >> 21) & 0x00FFFFFFFFFFFFFF);
+                                        targetValue = targetValue + slide;
+                                        *(uint64_t*)address = targetValue;
+                                    }
+                                }
+
+                                // The delta is bits [51..61]
+                                // And bit 62 is to tell us if we are a rebase (0) or bind (1)
+                                value &= ~(1ULL << 62);
+                                delta = ( value & 0x3FF8000000000000 ) >> 51;
+                                segOffset += delta * sizeof(uintptr_t);
+                            } while ( delta != 0 );
+                            break;
+                        }
+                        default:
+                            throw "unknown threaded bind subopcode";
+                    }
+                    break;
+                default:
+                    throw "unknown bind opcode";
+            }
+        }
+        return;
+    }
+
 #if __x86_64__
        const struct macho_segment_command* firstWritableSeg = NULL;
 #endif
@@ -133,15 +408,13 @@ static void rebaseDyld(const struct macho_header* mh, intptr_t slide)
                        case LC_SEGMENT_COMMAND:
                                {
                                        const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
-                                       if ( strcmp(seg->segname, "__LINKEDIT") == 0 )
-                                               linkEditSeg = seg;
                                        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_NON_LAZY_SYMBOL_POINTERS ) {
                                                        // rebase non-lazy pointers (which all point internal to dyld, since dyld uses no shared libraries)
-                                                       const uint32_t pointerCount = sect->size / sizeof(uintptr_t);
+                                                       const uint32_t pointerCount = (uint32_t)(sect->size / sizeof(uintptr_t));
                                                        uintptr_t* const symbolPointers = (uintptr_t*)(sect->addr + slide);
                                                        for (uint32_t j=0; j < pointerCount; ++j) {
                                                                symbolPointers[j] += slide;
@@ -163,6 +436,8 @@ static void rebaseDyld(const struct macho_header* mh, intptr_t slide)
        
        // use reloc's to rebase all random data pointers
 #if __x86_64__
+    if ( firstWritableSeg == NULL )
+        throw "no writable segment in dyld";
        const uintptr_t relocBase = firstWritableSeg->vmaddr + slide;
 #else
        const uintptr_t relocBase = (uintptr_t)mh;
@@ -170,10 +445,6 @@ static void rebaseDyld(const struct macho_header* mh, intptr_t slide)
        const relocation_info* const relocsStart = (struct relocation_info*)(linkEditSeg->vmaddr + slide + dynamicSymbolTable->locreloff - linkEditSeg->fileoff);
        const relocation_info* const relocsEnd = &relocsStart[dynamicSymbolTable->nlocrel];
        for (const relocation_info* reloc=relocsStart; reloc < relocsEnd; ++reloc) {
-       #if __ppc__ || __ppc64__ || __i36__
-               if ( (reloc->r_address & R_SCATTERED) != 0 )
-                       throw "scattered relocation in dyld";
-       #endif
                if ( reloc->r_length != RELOC_SIZE ) 
                        throw "relocation in dyld has wrong size";
 
@@ -186,177 +457,32 @@ static void rebaseDyld(const struct macho_header* mh, intptr_t slide)
 }
 
 
-//
-// For some reason the kernel loads dyld with __TEXT and __LINKEDIT writable
-// rdar://problem/3702311 
-//
-static void segmentProtectDyld(const struct macho_header* mh, intptr_t slide)
-{
-       const uint32_t cmd_count = mh->ncmds;
-       const struct load_command* const cmds = (struct load_command*)(((char*)mh)+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;
-                                       vm_address_t addr = seg->vmaddr + slide;
-                                       vm_size_t size = seg->vmsize;
-                                       const bool setCurrentPermissions = false;
-                                       vm_protect(mach_task_self(), addr, size, setCurrentPermissions, seg->initprot);
-                                       //dyld::log("dyld: segment %s, 0x%08X -> 0x%08X, set to %d\n", seg->segname, addr, addr+size-1, seg->initprot);
-                               }
-                               break;
-               }
-               cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
-       }
-       
-}
-
-
-//
-// re-map the main executable to a new random address
-//
-static const struct macho_header* randomizeExecutableLoadAddress(const struct macho_header* orgMH, const char* envp[], uintptr_t* appsSlide)
-{
-#if __ppc__
-       // don't slide PIE programs running under rosetta
-       if ( dyld::isRosetta() )
-               return orgMH;
-#endif
-       // environment variable DYLD_NO_PIE can disable PIE
-       for(const char** p = envp; *p != NULL; p++) {
-               if ( strncmp(*p, "DYLD_NO_PIE=", 12) == 0 )
-                       return orgMH;
-       }
-       
-       // count segments
-       uint32_t segCount = 0;
-       const uint32_t cmd_count = orgMH->ncmds;
-       const struct load_command* const cmds = (struct load_command*)(((char*)orgMH)+sizeof(macho_header));
-       const struct load_command* cmd = cmds;
-       for (uint32_t i = 0; i < cmd_count; ++i) {
-               if ( cmd->cmd == LC_SEGMENT_COMMAND ) {
-                       const struct macho_segment_command* segCmd = (struct macho_segment_command*)cmd;
-                       // page-zero and custom stacks don't move
-                       if ( (strcmp(segCmd->segname, "__PAGEZERO") != 0) && (strcmp(segCmd->segname, "__UNIXSTACK") != 0) ) 
-                               ++segCount;
-               }
-               cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
-       }
-       
-       // make copy of segment info
-       macho_segment_command segs[segCount];
-       uint32_t index = 0;
-       uintptr_t highestAddressUsed = 0;
-       uintptr_t lowestAddressUsed = UINTPTR_MAX;
-       cmd = cmds;
-       for (uint32_t i = 0; i < cmd_count; ++i) {
-               if ( cmd->cmd == LC_SEGMENT_COMMAND ) {
-                       const struct macho_segment_command* segCmd = (struct macho_segment_command*)cmd;
-                       if ( (strcmp(segCmd->segname, "__PAGEZERO") != 0) && (strcmp(segCmd->segname, "__UNIXSTACK") != 0) ) {
-                               segs[index++] = *segCmd;
-                               if ( (segCmd->vmaddr + segCmd->vmsize) > highestAddressUsed )
-                                       highestAddressUsed = ((segCmd->vmaddr + segCmd->vmsize) + 4095) & -4096;
-                               if ( segCmd->vmaddr < lowestAddressUsed )
-                                       lowestAddressUsed = segCmd->vmaddr;
-                               // do nothing if kernel has already randomized load address
-                               if ( (strcmp(segCmd->segname, "__TEXT") == 0) && (segCmd->vmaddr != (uintptr_t)orgMH) )
-                                       return orgMH;
-                       }
-               }
-               cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
-       }
-       
-       // choose a random new base address
-#if __LP64__
-       uintptr_t highestAddressPossible = highestAddressUsed + 0x100000000ULL;
-#elif __arm__
-       uintptr_t highestAddressPossible = 0x2fe00000;
-#else
-       uintptr_t highestAddressPossible = 0x80000000;
-#endif
-       uintptr_t sizeNeeded = highestAddressUsed-lowestAddressUsed;
-       if ( (highestAddressPossible-sizeNeeded) < highestAddressUsed ) {
-               // new and old segments will overlap 
-               // need better algorithm for remapping
-               // punt and don't re-map
-               return orgMH;
-       }
-       uintptr_t possibleRange = (highestAddressPossible-sizeNeeded) - highestAddressUsed;
-       uintptr_t newBaseAddress = highestAddressUsed + ((arc4random() % possibleRange) & -4096);
-       
-       vm_address_t addr = newBaseAddress;
-       // reserve new address range
-       if ( vm_allocate(mach_task_self(), &addr, sizeNeeded, VM_FLAGS_FIXED) == KERN_SUCCESS ) {
-               // copy each segment to new address
-               for (uint32_t i = 0; i < segCount; ++i) {
-                       uintptr_t newSegAddress = segs[i].vmaddr - lowestAddressUsed + newBaseAddress;
-                       if ( (vm_copy(mach_task_self(), segs[i].vmaddr, segs[i].vmsize, newSegAddress) != KERN_SUCCESS)
-               #if !__arm__  // work around for <rdar://problem/5736393>
-                               || (vm_protect(mach_task_self(), newSegAddress, segs[i].vmsize, true, segs[i].maxprot) != KERN_SUCCESS) 
-               #endif
-                               || (vm_protect(mach_task_self(), newSegAddress, segs[i].vmsize, false, segs[i].initprot) != KERN_SUCCESS) ) {
-                               // can't copy so dealloc new region and run with original base address
-                               vm_deallocate(mach_task_self(), newBaseAddress, sizeNeeded);
-                               dyld::warn("could not relocate position independent executable\n");
-                               return orgMH;
-                       }
-               }
-               // unmap original segments
-               vm_deallocate(mach_task_self(), lowestAddressUsed, highestAddressUsed-lowestAddressUsed);
-       
-               // run with newly mapped executable
-               *appsSlide = newBaseAddress - lowestAddressUsed;
-               return (const struct macho_header*)newBaseAddress;
-       }
-       
-       // can't get new range, so don't slide to random address
-       return orgMH;
-}
-
-
-extern "C" void dyld_exceptions_init(const struct macho_header*, uintptr_t slide); // in dyldExceptions.cpp
 extern "C" void mach_init();
-
-//
-// _pthread_keys is partitioned in a lower part that dyld will use; libSystem
-// will use the upper part.  We set __pthread_tsd_first to 1 as the start of
-// the lower part.  Libc will take #1 and c++ exceptions will take #2.  There
-// is one free key=3 left.
-//
-extern "C" {
-       extern int __pthread_tsd_first;
-       extern void _pthread_keys_init();
-}
+extern "C" void __guard_setup(const char* apple[]);
 
 
 //
 //  This is code to bootstrap dyld.  This work in normally done for a program by dyld and crt.
 //  In dyld we have to do this manually.
 //
-uintptr_t start(const struct macho_header* appsMachHeader, int argc, const char* argv[], intptr_t slide)
+uintptr_t start(const struct macho_header* appsMachHeader, int argc, const char* argv[], 
+                               intptr_t slide, const struct macho_header* dyldsMachHeader,
+                               uintptr_t* startGlue)
 {
-       // _mh_dylinker_header is magic symbol defined by static linker (ld), see <mach-o/ldsyms.h>
-       const struct macho_header* dyldsMachHeader =  (const struct macho_header*)(((char*)&_mh_dylinker_header)+slide);
-       
        // if kernel had to slide dyld, we need to fix up load sensitive locations
        // we have to do this before using any global variables
-       if ( slide != 0 ) {
-               rebaseDyld(dyldsMachHeader, slide);
-       }
-       
-       uintptr_t appsSlide = 0;
-               
-       // enable C++ exceptions to work inside dyld
-       dyld_exceptions_init(dyldsMachHeader, slide);
-       
+    slide = slideOfMainExecutable(dyldsMachHeader);
+    bool shouldRebase = slide != 0;
+#if __has_feature(ptrauth_calls)
+    shouldRebase = true;
+#endif
+    if ( shouldRebase ) {
+        rebaseDyld(dyldsMachHeader, slide);
+    }
+
        // allow dyld to use mach messaging
        mach_init();
 
-       // set protection on segments (has to be done after mach_init)
-       segmentProtectDyld(dyldsMachHeader, slide);
-       
        // kernel sets up env pointer to be just past end of agv array
        const char** envp = &argv[argc+1];
        
@@ -365,18 +491,55 @@ uintptr_t start(const struct macho_header* appsMachHeader, int argc, const char*
        while(*apple != NULL) { ++apple; }
        ++apple;
 
+       // set up random value for stack canary
+       __guard_setup(apple);
+
+#if DYLD_INITIALIZER_SUPPORT
        // run all C++ initializers inside dyld
        runDyldInitializers(dyldsMachHeader, slide, argc, argv, envp, apple);
-       
-       // if main executable was linked -pie, then randomize its load address
-       if ( appsMachHeader->flags & MH_PIE )
-               appsMachHeader = randomizeExecutableLoadAddress(appsMachHeader, envp, &appsSlide);
-       
+#endif
+
        // now that we are done bootstrapping dyld, call dyld's main
-       return dyld::_main(appsMachHeader, appsSlide, argc, argv, envp, apple);
+       uintptr_t appsSlide = slideOfMainExecutable(appsMachHeader);
+       return dyld::_main(appsMachHeader, appsSlide, argc, argv, envp, apple, startGlue);
 }
 
 
+#if TARGET_IPHONE_SIMULATOR
+
+extern "C" uintptr_t start_sim(int argc, const char* argv[], const char* envp[], const char* apple[],
+                                                       const macho_header* mainExecutableMH, const macho_header* dyldMH, uintptr_t dyldSlide,
+                                                       const dyld::SyscallHelpers*, uintptr_t* startGlue);
+                                       
+                                       
+uintptr_t start_sim(int argc, const char* argv[], const char* envp[], const char* apple[],
+                                       const macho_header* mainExecutableMH, const macho_header* dyldMH, uintptr_t dyldSlide,
+                                       const dyld::SyscallHelpers* sc, uintptr_t* startGlue)
+{
+       // if simulator dyld loaded slid, it needs to rebase itself
+       // we have to do this before using any global variables
+       if ( dyldSlide != 0 ) {
+               rebaseDyld(dyldMH, dyldSlide);
+       }
+
+       // save table of syscall pointers
+       gSyscallHelpers = sc;
+       
+       // allow dyld to use mach messaging
+       mach_init();
+
+       // set up random value for stack canary
+       __guard_setup(apple);
+
+       // setup gProcessInfo to point to host dyld's struct
+       dyld::gProcessInfo = (struct dyld_all_image_infos*)(sc->getProcessInfo());
+       syncProcessInfo();
+
+       // now that we are done bootstrapping dyld, call dyld's main
+       uintptr_t appsSlide = slideOfMainExecutable(mainExecutableMH);
+       return dyld::_main(mainExecutableMH, appsSlide, argc, argv, envp, apple, startGlue);
+}
+#endif
 
 
 } // end of namespace