src/dyldInitialization.cpp

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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 <sys/mman.h>
  31 #include <mach/mach.h>
  32
  33 #include "dyld2.h"
  34 #include "dyldSyscallInterface.h"
  35 #include "MachOAnalyzer.h"
  36 #include "Tracing.h"
  37
  38 // from libc.a
  39 extern "C" void mach_init();
  40 extern "C" void __guard_setup(const char* apple[]);
  41 extern "C" void _subsystem_init(const char* apple[]);
  42
  43 // from dyld_debugger.cpp
  44 extern void syncProcessInfo();
  45
  46 const dyld::SyscallHelpers* gSyscallHelpers = NULL;
  47
  48
  49 //
  50 //  Code to bootstrap dyld into a runnable state
  51 //
  52 //
  53
  54 namespace dyldbootstrap {
  55
  56
  57 // currently dyld has no initializers, but if some come back, set this to non-zero
  58 #define DYLD_INITIALIZER_SUPPORT  0
  59
  60
  61 #if DYLD_INITIALIZER_SUPPORT
  62
  63 typedef void (*Initializer)(int argc, const char* argv[], const char* envp[], const char* apple[]);
  64
  65 extern const Initializer  inits_start  __asm("section$start$__DATA$__mod_init_func");
  66 extern const Initializer  inits_end    __asm("section$end$__DATA$__mod_init_func");
  67
  68 //
  69 // For a regular executable, the crt code calls dyld to run the executables initializers.
  70 // For a static executable, crt directly runs the initializers.
  71 // dyld (should be static) but is a dynamic executable and needs this hack to run its own initializers.
  72 // We pass argc, argv, etc in case libc.a uses those arguments
  73 //
  74 static void runDyldInitializers(int argc, const char* argv[], const char* envp[], const char* apple[])
  75 {
  76         for (const Initializer* p = &inits_start; p < &inits_end; ++p) {
  77                 (*p)(argc, argv, envp, apple);
  78         }
  79 }
  80 #endif // DYLD_INITIALIZER_SUPPORT
  81
  82
  83 //
  84 // On disk, all pointers in dyld's DATA segment are chained together.
  85 // They need to be fixed up to be real pointers to run.
  86 //
  87 static void rebaseDyld(const dyld3::MachOLoaded* dyldMH)
  88 {
  89     // walk all fixups chains and rebase dyld
  90     const dyld3::MachOAnalyzer* ma = (dyld3::MachOAnalyzer*)dyldMH;
  91     assert(ma->hasChainedFixups());
  92     uintptr_t slide = (long)ma; // all fixup chain based images have a base address of zero, so slide == load address
  93     __block Diagnostics diag;
  94     ma->withChainStarts(diag, 0, ^(const dyld_chained_starts_in_image* starts) {
  95         ma->fixupAllChainedFixups(diag, starts, slide, dyld3::Array<const void*>(), nullptr);
  96     });
  97     diag.assertNoError();
  98
  99     // now that rebasing done, initialize mach/syscall layer
 100     mach_init();
 101
 102     // <rdar://47805386> mark __DATA_CONST segment in dyld as read-only (once fixups are done)
 103     ma->forEachSegment(^(const dyld3::MachOFile::SegmentInfo& info, bool& stop) {
 104         if ( info.readOnlyData ) {
 105             ::mprotect(((uint8_t*)(dyldMH))+info.vmAddr, (size_t)info.vmSize, VM_PROT_READ);
 106         }
 107     });
 108 }
 109
 110
 111
 112 //
 113 //  This is code to bootstrap dyld.  This work in normally done for a program by dyld and crt.
 114 //  In dyld we have to do this manually.
 115 //
 116 uintptr_t start(const dyld3::MachOLoaded* appsMachHeader, int argc, const char* argv[],
 117                                 const dyld3::MachOLoaded* dyldsMachHeader, uintptr_t* startGlue)
 118 {
 119
 120     // Emit kdebug tracepoint to indicate dyld bootstrap has started <rdar://46878536>
 121     dyld3::kdebug_trace_dyld_marker(DBG_DYLD_TIMING_BOOTSTRAP_START, 0, 0, 0, 0);
 122
 123         // if kernel had to slide dyld, we need to fix up load sensitive locations
 124         // we have to do this before using any global variables
 125     rebaseDyld(dyldsMachHeader);
 126
 127         // kernel sets up env pointer to be just past end of agv array
 128         const char** envp = &argv[argc+1];
 129
 130         // kernel sets up apple pointer to be just past end of envp array
 131         const char** apple = envp;
 132         while(*apple != NULL) { ++apple; }
 133         ++apple;
 134
 135         // set up random value for stack canary
 136         __guard_setup(apple);
 137
 138 #if DYLD_INITIALIZER_SUPPORT
 139         // run all C++ initializers inside dyld
 140         runDyldInitializers(argc, argv, envp, apple);
 141 #endif
 142
 143         _subsystem_init(apple);
 144
 145         // now that we are done bootstrapping dyld, call dyld's main
 146         uintptr_t appsSlide = appsMachHeader->getSlide();
 147         return dyld::_main((macho_header*)appsMachHeader, appsSlide, argc, argv, envp, apple, startGlue);
 148 }
 149
 150
 151 #if TARGET_OS_SIMULATOR
 152
 153 extern "C" uintptr_t start_sim(int argc, const char* argv[], const char* envp[], const char* apple[],
 154                                                         const dyld3::MachOLoaded* mainExecutableMH, const dyld3::MachOLoaded* dyldMH, uintptr_t dyldSlide,
 155                                                         const dyld::SyscallHelpers*, uintptr_t* startGlue);
 156
 157
 158 uintptr_t start_sim(int argc, const char* argv[], const char* envp[], const char* apple[],
 159                                         const dyld3::MachOLoaded* mainExecutableMH, const dyld3::MachOLoaded* dyldSimMH, uintptr_t dyldSlide,
 160                                         const dyld::SyscallHelpers* sc, uintptr_t* startGlue)
 161 {
 162     // save table of syscall pointers
 163     gSyscallHelpers = sc;
 164
 165         // dyld_sim uses chained rebases, so it always need to be fixed up
 166     rebaseDyld(dyldSimMH);
 167
 168         // set up random value for stack canary
 169         __guard_setup(apple);
 170
 171         // setup gProcessInfo to point to host dyld's struct
 172         dyld::gProcessInfo = (struct dyld_all_image_infos*)(sc->getProcessInfo());
 173         syncProcessInfo();
 174
 175         // now that we are done bootstrapping dyld, call dyld's main
 176     uintptr_t appsSlide = mainExecutableMH->getSlide();
 177         return dyld::_main((macho_header*)mainExecutableMH, appsSlide, argc, argv, envp, apple, startGlue);
 178 }
 179 #endif
 180
 181
 182 } // end of namespace
 183
 184
 185
 186