src/dyldInitialization.cpp

   1 /* -*- mode: C++; c-basic-offset: 4; tab-width: 4 -*-
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  24
  25 #define __STDC_LIMIT_MACROS
  26 #include <stdint.h>
  27 #include <stddef.h>
  28 #include <string.h>
  29 #include <stdlib.h>
  30 #include <Availability.h>
  31 #include <mach/mach.h>
  32 #include <mach-o/loader.h>
  33 #include <mach-o/ldsyms.h>
  34 #include <mach-o/reloc.h>
  35 #if __x86_64__
  36         #include <mach-o/x86_64/reloc.h>
  37 #endif
  38 #include "dyld.h"
  39 #include "dyldSyscallInterface.h"
  40
  41 // from dyld_gdb.cpp
  42 extern void addImagesToAllImages(uint32_t infoCount, const dyld_image_info info[]);
  43 extern void syncProcessInfo();
  44
  45 #ifndef MH_PIE
  46         #define MH_PIE 0x200000
  47 #endif
  48
  49 // currently dyld has no initializers, but if some come back, set this to non-zero
  50 #define DYLD_INITIALIZER_SUPPORT  0
  51
  52 #if __LP64__
  53         #define LC_SEGMENT_COMMAND              LC_SEGMENT_64
  54         #define macho_segment_command   segment_command_64
  55         #define macho_section                   section_64
  56         #define RELOC_SIZE                              3
  57 #else
  58         #define LC_SEGMENT_COMMAND              LC_SEGMENT
  59         #define macho_segment_command   segment_command
  60         #define macho_section                   section
  61         #define RELOC_SIZE                              2
  62 #endif
  63
  64 #if __x86_64__
  65         #define POINTER_RELOC X86_64_RELOC_UNSIGNED
  66 #else
  67         #define POINTER_RELOC GENERIC_RELOC_VANILLA
  68 #endif
  69
  70
  71 #if TARGET_IPHONE_SIMULATOR
  72 const dyld::SyscallHelpers* gSyscallHelpers = NULL;
  73 #endif
  74
  75
  76 //
  77 //  Code to bootstrap dyld into a runnable state
  78 //
  79 //
  80
  81 namespace dyldbootstrap {
  82
  83
  84
  85 #if DYLD_INITIALIZER_SUPPORT
  86
  87 typedef void (*Initializer)(int argc, const char* argv[], const char* envp[], const char* apple[]);
  88
  89 extern const Initializer  inits_start  __asm("section$start$__DATA$__mod_init_func");
  90 extern const Initializer  inits_end    __asm("section$end$__DATA$__mod_init_func");
  91
  92 //
  93 // For a regular executable, the crt code calls dyld to run the executables initializers.
  94 // For a static executable, crt directly runs the initializers.
  95 // dyld (should be static) but is a dynamic executable and needs this hack to run its own initializers.
  96 // We pass argc, argv, etc in case libc.a uses those arguments
  97 //
  98 static void runDyldInitializers(const struct macho_header* mh, intptr_t slide, int argc, const char* argv[], const char* envp[], const char* apple[])
  99 {
 100         for (const Initializer* p = &inits_start; p < &inits_end; ++p) {
 101                 (*p)(argc, argv, envp, apple);
 102         }
 103 }
 104 #endif // DYLD_INITIALIZER_SUPPORT
 105
 106
 107 //
 108 //  The kernel may have slid a Position Independent Executable
 109 //
 110 static uintptr_t slideOfMainExecutable(const struct macho_header* mh)
 111 {
 112         const uint32_t cmd_count = mh->ncmds;
 113         const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header));
 114         const struct load_command* cmd = cmds;
 115         for (uint32_t i = 0; i < cmd_count; ++i) {
 116                 if ( cmd->cmd == LC_SEGMENT_COMMAND ) {
 117                         const struct macho_segment_command* segCmd = (struct macho_segment_command*)cmd;
 118                         if ( strcmp(segCmd->segname, "__TEXT") == 0 ) {
 119                                 return (uintptr_t)mh - segCmd->vmaddr;
 120                         }
 121                 }
 122                 cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
 123         }
 124         return 0;
 125 }
 126
 127
 128 //
 129 // If the kernel does not load dyld at its preferred address, we need to apply
 130 // fixups to various initialized parts of the __DATA segment
 131 //
 132 static void rebaseDyld(const struct macho_header* mh, intptr_t slide)
 133 {
 134         // rebase non-lazy pointers (which all point internal to dyld, since dyld uses no shared libraries)
 135         // and get interesting pointers into dyld
 136         const uint32_t cmd_count = mh->ncmds;
 137         const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header));
 138         const struct load_command* cmd = cmds;
 139         const struct macho_segment_command* linkEditSeg = NULL;
 140 #if __x86_64__
 141         const struct macho_segment_command* firstWritableSeg = NULL;
 142 #endif
 143         const struct dysymtab_command* dynamicSymbolTable = NULL;
 144         for (uint32_t i = 0; i < cmd_count; ++i) {
 145                 switch (cmd->cmd) {
 146                         case LC_SEGMENT_COMMAND:
 147                                 {
 148                                         const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
 149                                         if ( strcmp(seg->segname, "__LINKEDIT") == 0 )
 150                                                 linkEditSeg = seg;
 151                                         const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
 152                                         const struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
 153                                         for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
 154                                                 const uint8_t type = sect->flags & SECTION_TYPE;
 155                                                 if ( type == S_NON_LAZY_SYMBOL_POINTERS ) {
 156                                                         // rebase non-lazy pointers (which all point internal to dyld, since dyld uses no shared libraries)
 157                                                         const uint32_t pointerCount = (uint32_t)(sect->size / sizeof(uintptr_t));
 158                                                         uintptr_t* const symbolPointers = (uintptr_t*)(sect->addr + slide);
 159                                                         for (uint32_t j=0; j < pointerCount; ++j) {
 160                                                                 symbolPointers[j] += slide;
 161                                                         }
 162                                                 }
 163                                         }
 164 #if __x86_64__
 165                                         if ( (firstWritableSeg == NULL) && (seg->initprot & VM_PROT_WRITE) )
 166                                                 firstWritableSeg = seg;
 167 #endif
 168                                 }
 169                                 break;
 170                         case LC_DYSYMTAB:
 171                                 dynamicSymbolTable = (struct dysymtab_command *)cmd;
 172                                 break;
 173                 }
 174                 cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
 175         }
 176
 177         // use reloc's to rebase all random data pointers
 178 #if __x86_64__
 179         const uintptr_t relocBase = firstWritableSeg->vmaddr + slide;
 180 #else
 181         const uintptr_t relocBase = (uintptr_t)mh;
 182 #endif
 183         const relocation_info* const relocsStart = (struct relocation_info*)(linkEditSeg->vmaddr + slide + dynamicSymbolTable->locreloff - linkEditSeg->fileoff);
 184         const relocation_info* const relocsEnd = &relocsStart[dynamicSymbolTable->nlocrel];
 185         for (const relocation_info* reloc=relocsStart; reloc < relocsEnd; ++reloc) {
 186                 if ( reloc->r_length != RELOC_SIZE )
 187                         throw "relocation in dyld has wrong size";
 188
 189                 if ( reloc->r_type != POINTER_RELOC )
 190                         throw "relocation in dyld has wrong type";
 191
 192                 // update pointer by amount dyld slid
 193                 *((uintptr_t*)(reloc->r_address + relocBase)) += slide;
 194         }
 195 }
 196
 197
 198 extern "C" void mach_init();
 199 extern "C" void __guard_setup(const char* apple[]);
 200
 201
 202 //
 203 //  This is code to bootstrap dyld.  This work in normally done for a program by dyld and crt.
 204 //  In dyld we have to do this manually.
 205 //
 206 uintptr_t start(const struct macho_header* appsMachHeader, int argc, const char* argv[],
 207                                 intptr_t slide, const struct macho_header* dyldsMachHeader,
 208                                 uintptr_t* startGlue)
 209 {
 210         // if kernel had to slide dyld, we need to fix up load sensitive locations
 211         // we have to do this before using any global variables
 212         if ( slide != 0 ) {
 213                 rebaseDyld(dyldsMachHeader, slide);
 214         }
 215
 216         // allow dyld to use mach messaging
 217         mach_init();
 218
 219         // kernel sets up env pointer to be just past end of agv array
 220         const char** envp = &argv[argc+1];
 221
 222         // kernel sets up apple pointer to be just past end of envp array
 223         const char** apple = envp;
 224         while(*apple != NULL) { ++apple; }
 225         ++apple;
 226
 227         // set up random value for stack canary
 228         __guard_setup(apple);
 229
 230 #if DYLD_INITIALIZER_SUPPORT
 231         // run all C++ initializers inside dyld
 232         runDyldInitializers(dyldsMachHeader, slide, argc, argv, envp, apple);
 233 #endif
 234
 235         // now that we are done bootstrapping dyld, call dyld's main
 236         uintptr_t appsSlide = slideOfMainExecutable(appsMachHeader);
 237         return dyld::_main(appsMachHeader, appsSlide, argc, argv, envp, apple, startGlue);
 238 }
 239
 240
 241 #if TARGET_IPHONE_SIMULATOR
 242
 243 extern "C" uintptr_t start_sim(int argc, const char* argv[], const char* envp[], const char* apple[],
 244                                                         const macho_header* mainExecutableMH, const macho_header* dyldMH, uintptr_t dyldSlide,
 245                                                         const dyld::SyscallHelpers*, uintptr_t* startGlue);
 246
 247
 248 uintptr_t start_sim(int argc, const char* argv[], const char* envp[], const char* apple[],
 249                                         const macho_header* mainExecutableMH, const macho_header* dyldMH, uintptr_t dyldSlide,
 250                                         const dyld::SyscallHelpers* sc, uintptr_t* startGlue)
 251 {
 252         // if simulator dyld loaded slid, it needs to rebase itself
 253         // we have to do this before using any global variables
 254         if ( dyldSlide != 0 ) {
 255                 rebaseDyld(dyldMH, dyldSlide);
 256         }
 257
 258         // save table of syscall pointers
 259         gSyscallHelpers = sc;
 260
 261         // allow dyld to use mach messaging
 262         mach_init();
 263
 264         // set up random value for stack canary
 265         __guard_setup(apple);
 266
 267         // setup gProcessInfo to point to host dyld's struct
 268         dyld::gProcessInfo = (struct dyld_all_image_infos*)(sc->getProcessInfo());
 269         syncProcessInfo();
 270
 271         // now that we are done bootstrapping dyld, call dyld's main
 272         uintptr_t appsSlide = slideOfMainExecutable(mainExecutableMH);
 273         return dyld::_main(mainExecutableMH, appsSlide, argc, argv, envp, apple, startGlue);
 274 }
 275 #endif
 276
 277
 278 } // end of namespace
 279
 280
 281
 282