src/ld/passes/got.cpp

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  24
  25
  26 #include <stdint.h>
  27 #include <math.h>
  28 #include <unistd.h>
  29 #include <dlfcn.h>
  30
  31 #include <vector>
  32 #include <map>
  33
  34 #include "MachOFileAbstraction.hpp"
  35 #include "ld.hpp"
  36 #include "got.h"
  37 #include "configure.h"
  38
  39 namespace ld {
  40 namespace passes {
  41 namespace got {
  42
  43 class File; // forward reference
  44
  45 class GOTEntryAtom : public ld::Atom {
  46 public:
  47                                                                                         GOTEntryAtom(ld::Internal& internal, const ld::Atom* target, bool weakImport, bool is64)
  48                                 : ld::Atom(_s_section, ld::Atom::definitionRegular, ld::Atom::combineNever,
  49                                                         ld::Atom::scopeLinkageUnit, ld::Atom::typeNonLazyPointer,
  50                                                         symbolTableNotIn, false, false, false, (is64 ? ld::Atom::Alignment(3) : ld::Atom::Alignment(2))),
  51                                 _fixup(0, ld::Fixup::k1of1, (is64 ? ld::Fixup::kindStoreTargetAddressLittleEndian64 : ld::Fixup::kindStoreTargetAddressLittleEndian32), target),
  52                                 _target(target),
  53                                 _is64(is64)
  54                                         { _fixup.weakImport = weakImport; internal.addAtom(*this); }
  55
  56         virtual const ld::File*                                 file() const                                    { return NULL; }
  57         virtual const char*                                             name() const                                    { return _target->name(); }
  58         virtual uint64_t                                                size() const                                    { return (_is64 ? 8 : 4); }
  59         virtual uint64_t                                                objectAddress() const                   { return 0; }
  60         virtual void                                                    copyRawContent(uint8_t buffer[]) const { }
  61         virtual void                                                    setScope(Scope)                                 { }
  62         virtual ld::Fixup::iterator                             fixupsBegin() const                             { return &_fixup; }
  63         virtual ld::Fixup::iterator                             fixupsEnd()     const                           { return &((ld::Fixup*)&_fixup)[1]; }
  64
  65 private:
  66         mutable ld::Fixup                                               _fixup;
  67         const ld::Atom*                                                 _target;
  68         bool                                                                    _is64;
  69
  70         static ld::Section                                              _s_section;
  71 };
  72
  73 ld::Section GOTEntryAtom::_s_section("__DATA", "__got", ld::Section::typeNonLazyPointer);
  74
  75
  76 static bool gotFixup(const Options& opts, ld::Internal& internal, const ld::Atom* targetOfGOT, const ld::Fixup* fixup, bool* optimizable)
  77 {
  78         switch (fixup->kind) {
  79                 case ld::Fixup::kindStoreTargetAddressX86PCRel32GOTLoad:
  80 #if SUPPORT_ARCH_arm64
  81                 case ld::Fixup::kindStoreTargetAddressARM64GOTLoadPage21:
  82                 case ld::Fixup::kindStoreTargetAddressARM64GOTLoadPageOff12:
  83 #endif
  84                         // start by assuming this can be optimized
  85                         *optimizable = true;
  86                         // cannot do LEA optimization if target is in another dylib
  87                         if ( targetOfGOT->definition() == ld::Atom::definitionProxy )
  88                                 *optimizable = false;
  89                         // cannot do LEA optimization if target in __huge section
  90                         if ( internal.usingHugeSections && (targetOfGOT->size() > 1024*1024)
  91                                                                                         && (   (targetOfGOT->section().type() == ld::Section::typeZeroFill)
  92                                                                                                 || (targetOfGOT->section().type() == ld::Section::typeTentativeDefs)) ) {
  93                                 *optimizable = false;
  94                         }
  95                         if ( targetOfGOT->scope() == ld::Atom::scopeGlobal ) {
  96                                 // cannot do LEA optimization if target is weak exported symbol
  97                                 if ( (targetOfGOT->definition() == ld::Atom::definitionRegular) && (targetOfGOT->combine() == ld::Atom::combineByName) ) {
  98                                         switch ( opts.outputKind() ) {
  99                                                 case Options::kDynamicExecutable:
 100                                                 case Options::kDynamicLibrary:
 101                                                 case Options::kDynamicBundle:
 102                                                 case Options::kKextBundle:
 103                                                         *optimizable = false;
 104                                                         break;
 105                                                 case Options::kStaticExecutable:
 106                                                 case Options::kDyld:
 107                                                 case Options::kPreload:
 108                                                 case Options::kObjectFile:
 109                                                         break;
 110                                         }
 111                                 }
 112                                 // cannot do LEA optimization if target is interposable
 113                                 if ( opts.interposable(targetOfGOT->name()) )
 114                                         *optimizable = false;
 115                                 // cannot do LEA optimization if target is resolver function
 116                                 if ( targetOfGOT->contentType() == ld::Atom::typeResolver )
 117                                         *optimizable = false;
 118                                 // cannot do LEA optimization for flat-namespace
 119                                 if ( opts.nameSpace() != Options::kTwoLevelNameSpace )
 120                                         *optimizable = false;
 121                         }
 122                         else if ( targetOfGOT->scope() == ld::Atom::scopeLinkageUnit) {
 123                                 // <rdar://problem/12379969> don't do optimization if target is in custom segment
 124                                 if ( opts.sharedRegionEligible() ) {
 125                                         const char* segName = targetOfGOT->section().segmentName();
 126                                         if ( (strcmp(segName, "__TEXT") != 0) && (strcmp(segName, "__DATA") != 0) ) {
 127                                                 *optimizable = false;
 128                                         }
 129                                 }
 130                         }
 131                         return true;
 132                 case ld::Fixup::kindStoreX86PCRel32GOT:
 133 #if SUPPORT_ARCH_arm64
 134                 case ld::Fixup::kindStoreARM64PCRelToGOT:
 135 #endif
 136                         *optimizable = false;
 137                         return true;
 138                 case ld::Fixup::kindNoneGroupSubordinatePersonality:
 139                         *optimizable = false;
 140                         return true;
 141                 default:
 142                         break;
 143         }
 144
 145         return false;
 146 }
 147
 148 struct AtomByNameSorter
 149 {
 150          bool operator()(const ld::Atom* left, const ld::Atom* right)
 151          {
 152                   return (strcmp(left->name(), right->name()) < 0);
 153          }
 154 };
 155
 156 void doPass(const Options& opts, ld::Internal& internal)
 157 {
 158         const bool log = false;
 159
 160         // only make got section in final linked images
 161         if ( opts.outputKind() == Options::kObjectFile )
 162                 return;
 163
 164         // pre-fill gotMap with existing non-lazy pointers
 165         std::map<const ld::Atom*, const ld::Atom*> gotMap;
 166         for (ld::Internal::FinalSection* sect : internal.sections) {
 167                 if ( sect->type() != ld::Section::typeNonLazyPointer )
 168                         continue;
 169                 for (const ld::Atom* atom : sect->atoms) {
 170                         const ld::Atom* target = NULL;
 171                         for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 172                                 switch (fit->kind) {
 173                                 case ld::Fixup::kindStoreTargetAddressLittleEndian64:
 174                                 case ld::Fixup::kindStoreTargetAddressLittleEndian32:
 175                                         switch ( fit->binding ) {
 176                                                 case ld::Fixup::bindingsIndirectlyBound:
 177                                                         target = internal.indirectBindingTable[fit->u.bindingIndex];
 178                                                         break;
 179                                                 case ld::Fixup::bindingDirectlyBound:
 180                                                         target = fit->u.target;
 181                                                         break;
 182                                                 default:
 183                                                         fprintf(stderr, "non-pointer is got entry\n");
 184                                                         break;
 185                                         }
 186                                         break;
 187                                 default:
 188                                         break;
 189                                 }
 190                         }
 191                         if ( target != NULL ) {
 192                                 if (log) fprintf(stderr, "found existing got entry to %s\n", target->name());
 193                                 gotMap[target] = atom;
 194                         }
 195                 }
 196         }
 197
 198         // walk all atoms and fixups looking for GOT-able references
 199         // don't create GOT atoms during this loop because that could invalidate the sections iterator
 200         std::vector<const ld::Atom*> atomsReferencingGOT;
 201         std::map<const ld::Atom*,bool>          weakImportMap;
 202         atomsReferencingGOT.reserve(128);
 203         for (std::vector<ld::Internal::FinalSection*>::iterator sit=internal.sections.begin(); sit != internal.sections.end(); ++sit) {
 204                 ld::Internal::FinalSection* sect = *sit;
 205                 for (std::vector<const ld::Atom*>::iterator ait=sect->atoms.begin();  ait != sect->atoms.end(); ++ait) {
 206                         const ld::Atom* atom = *ait;
 207                         bool atomUsesGOT = false;
 208                         const ld::Atom* targetOfGOT = NULL;
 209                         bool targetIsWeakImport = false;
 210                         for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 211                                 if ( fit->firstInCluster() )
 212                                         targetOfGOT = NULL;
 213                                 switch ( fit->binding ) {
 214                                         case ld::Fixup::bindingsIndirectlyBound:
 215                                                 targetOfGOT = internal.indirectBindingTable[fit->u.bindingIndex];
 216                                                 targetIsWeakImport = fit->weakImport;
 217                                                 break;
 218                                         case ld::Fixup::bindingDirectlyBound:
 219                                                 targetOfGOT = fit->u.target;
 220                                                 targetIsWeakImport = fit->weakImport;
 221                                                 break;
 222                     default:
 223                         break;
 224                                 }
 225                                 bool optimizable;
 226                                 if ( !gotFixup(opts, internal, targetOfGOT, fit, &optimizable) )
 227                                         continue;
 228                                 if ( optimizable ) {
 229                                         // change from load of GOT entry to lea of target
 230                                         if ( log ) fprintf(stderr, "optimized GOT usage in %s to %s\n", atom->name(), targetOfGOT->name());
 231                                         switch ( fit->binding ) {
 232                                                 case ld::Fixup::bindingsIndirectlyBound:
 233                                                 case ld::Fixup::bindingDirectlyBound:
 234                                                         fit->binding = ld::Fixup::bindingDirectlyBound;
 235                                                         fit->u.target = targetOfGOT;
 236                                                         switch ( fit->kind ) {
 237                                                                 case ld::Fixup::kindStoreTargetAddressX86PCRel32GOTLoad:
 238                                                                         fit->kind = ld::Fixup::kindStoreTargetAddressX86PCRel32GOTLoadNowLEA;
 239                                                                         break;
 240 #if SUPPORT_ARCH_arm64
 241                                                                 case ld::Fixup::kindStoreTargetAddressARM64GOTLoadPage21:
 242                                                                         fit->kind = ld::Fixup::kindStoreTargetAddressARM64GOTLeaPage21;
 243                                                                         break;
 244                                                                 case ld::Fixup::kindStoreTargetAddressARM64GOTLoadPageOff12:
 245                                                                         fit->kind = ld::Fixup::kindStoreTargetAddressARM64GOTLeaPageOff12;
 246                                                                         break;
 247 #endif
 248                                                                 default:
 249                                                                         assert(0 && "unsupported GOT reference kind");
 250                                                                         break;
 251                                                         }
 252                                                         break;
 253                                                 default:
 254                                                         assert(0 && "unsupported GOT reference");
 255                                                         break;
 256                                         }
 257                                 }
 258                                 else {
 259                                         // remember that we need to use GOT in this function
 260                                         if ( log ) fprintf(stderr, "found GOT use in %s\n", atom->name());
 261                                         if ( !atomUsesGOT ) {
 262                                                 atomsReferencingGOT.push_back(atom);
 263                                                 atomUsesGOT = true;
 264                                         }
 265                                         if ( gotMap.count(targetOfGOT) == 0 )
 266                                                 gotMap[targetOfGOT] = NULL;
 267                                         // record weak_import attribute
 268                                         std::map<const ld::Atom*,bool>::iterator pos = weakImportMap.find(targetOfGOT);
 269                                         if ( pos == weakImportMap.end() ) {
 270                                                 // target not in weakImportMap, so add
 271                                                 if ( log ) fprintf(stderr, "weakImportMap[%s] = %d\n", targetOfGOT->name(), targetIsWeakImport);
 272                                                 weakImportMap[targetOfGOT] = targetIsWeakImport;
 273                                         }
 274                                         else {
 275                                                 // target in weakImportMap, check for weakness mismatch
 276                                                 if ( pos->second != targetIsWeakImport ) {
 277                                                         // found mismatch
 278                                                         switch ( opts.weakReferenceMismatchTreatment() ) {
 279                                                                 case Options::kWeakReferenceMismatchError:
 280                                                                         throwf("mismatching weak references for symbol: %s", targetOfGOT->name());
 281                                                                 case Options::kWeakReferenceMismatchWeak:
 282                                                                         pos->second = true;
 283                                                                         break;
 284                                                                 case Options::kWeakReferenceMismatchNonWeak:
 285                                                                         pos->second = false;
 286                                                                         break;
 287                                                         }
 288                                                 }
 289                                         }
 290                                 }
 291                         }
 292                 }
 293         }
 294
 295         bool is64 = false;
 296         switch ( opts.architecture() ) {
 297 #if SUPPORT_ARCH_i386
 298                 case CPU_TYPE_I386:
 299                         is64 = false;
 300                         break;
 301 #endif
 302 #if SUPPORT_ARCH_x86_64
 303                 case CPU_TYPE_X86_64:
 304                         is64 = true;
 305                         break;
 306 #endif
 307 #if SUPPORT_ARCH_arm_any
 308                 case CPU_TYPE_ARM:
 309                         is64 = false;
 310                         break;
 311 #endif
 312 #if SUPPORT_ARCH_arm64
 313                 case CPU_TYPE_ARM64:
 314                         is64 = true;
 315                         break;
 316 #endif
 317         }
 318
 319         // make GOT entries
 320         for (auto& entry : gotMap) {
 321                 if ( entry.second == NULL ) {
 322                         entry.second = new GOTEntryAtom(internal, entry.first, weakImportMap[entry.first], is64);
 323                         if (log) fprintf(stderr, "making new GOT slot for %s, gotMap[%p] = %p\n", entry.first->name(), entry.first, entry.second);
 324                 }
 325         }
 326
 327
 328         // update atoms to use GOT entries
 329         for (std::vector<const ld::Atom*>::iterator it=atomsReferencingGOT.begin(); it != atomsReferencingGOT.end(); ++it) {
 330                 const ld::Atom* atom = *it;
 331                 const ld::Atom* targetOfGOT = NULL;
 332                 ld::Fixup::iterator fitThatSetTarget = NULL;
 333                 for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 334                         if ( fit->firstInCluster() ) {
 335                                 targetOfGOT = NULL;
 336                                 fitThatSetTarget = NULL;
 337                         }
 338                         switch ( fit->binding ) {
 339                                 case ld::Fixup::bindingsIndirectlyBound:
 340                                         targetOfGOT = internal.indirectBindingTable[fit->u.bindingIndex];
 341                                         fitThatSetTarget = fit;
 342                                         break;
 343                                 case ld::Fixup::bindingDirectlyBound:
 344                                         targetOfGOT = fit->u.target;
 345                                         fitThatSetTarget = fit;
 346                                         break;
 347                 default:
 348                     break;
 349                         }
 350                         bool optimizable;
 351                         if ( (targetOfGOT == NULL) || !gotFixup(opts, internal, targetOfGOT, fit, &optimizable) )
 352                                 continue;
 353                         if ( !optimizable ) {
 354                                 // GOT use not optimized away, update to bind to GOT entry
 355                                 assert(fitThatSetTarget != NULL);
 356                                 switch ( fitThatSetTarget->binding ) {
 357                                         case ld::Fixup::bindingsIndirectlyBound:
 358                                         case ld::Fixup::bindingDirectlyBound:
 359                                                 if ( log ) fprintf(stderr, "updating GOT use in %s to %s\n", atom->name(), targetOfGOT->name());
 360                                                 fitThatSetTarget->binding = ld::Fixup::bindingDirectlyBound;
 361                                                 fitThatSetTarget->u.target = gotMap[targetOfGOT];
 362                                                 break;
 363                                         default:
 364                                                 assert(0 && "unsupported GOT reference");
 365                                                 break;
 366                                 }
 367                         }
 368                 }
 369         }
 370
 371         // sort new atoms so links are consistent
 372         for (std::vector<ld::Internal::FinalSection*>::iterator sit=internal.sections.begin(); sit != internal.sections.end(); ++sit) {
 373                 ld::Internal::FinalSection* sect = *sit;
 374                 if ( sect->type() == ld::Section::typeNonLazyPointer ) {
 375                         std::sort(sect->atoms.begin(), sect->atoms.end(), AtomByNameSorter());
 376                 }
 377         }
 378 }
 379
 380
 381 } // namespace got
 382 } // namespace passes
 383 } // namespace ld