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         // walk all atoms and fixups looking for GOT-able references
 165         // don't create GOT atoms during this loop because that could invalidate the sections iterator
 166         std::vector<const ld::Atom*> atomsReferencingGOT;
 167         std::map<const ld::Atom*,ld::Atom*> gotMap;
 168         std::map<const ld::Atom*,bool>          weakImportMap;
 169         atomsReferencingGOT.reserve(128);
 170         for (std::vector<ld::Internal::FinalSection*>::iterator sit=internal.sections.begin(); sit != internal.sections.end(); ++sit) {
 171                 ld::Internal::FinalSection* sect = *sit;
 172                 for (std::vector<const ld::Atom*>::iterator ait=sect->atoms.begin();  ait != sect->atoms.end(); ++ait) {
 173                         const ld::Atom* atom = *ait;
 174                         bool atomUsesGOT = false;
 175                         const ld::Atom* targetOfGOT = NULL;
 176                         bool targetIsWeakImport = false;
 177                         for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 178                                 if ( fit->firstInCluster() )
 179                                         targetOfGOT = NULL;
 180                                 switch ( fit->binding ) {
 181                                         case ld::Fixup::bindingsIndirectlyBound:
 182                                                 targetOfGOT = internal.indirectBindingTable[fit->u.bindingIndex];
 183                                                 targetIsWeakImport = fit->weakImport;
 184                                                 break;
 185                                         case ld::Fixup::bindingDirectlyBound:
 186                                                 targetOfGOT = fit->u.target;
 187                                                 targetIsWeakImport = fit->weakImport;
 188                                                 break;
 189                     default:
 190                         break;
 191                                 }
 192                                 bool optimizable;
 193                                 if ( !gotFixup(opts, internal, targetOfGOT, fit, &optimizable) )
 194                                         continue;
 195                                 if ( optimizable ) {
 196                                         // change from load of GOT entry to lea of target
 197                                         if ( log ) fprintf(stderr, "optimized GOT usage in %s to %s\n", atom->name(), targetOfGOT->name());
 198                                         switch ( fit->binding ) {
 199                                                 case ld::Fixup::bindingsIndirectlyBound:
 200                                                 case ld::Fixup::bindingDirectlyBound:
 201                                                         fit->binding = ld::Fixup::bindingDirectlyBound;
 202                                                         fit->u.target = targetOfGOT;
 203                                                         switch ( fit->kind ) {
 204                                                                 case ld::Fixup::kindStoreTargetAddressX86PCRel32GOTLoad:
 205                                                                         fit->kind = ld::Fixup::kindStoreTargetAddressX86PCRel32GOTLoadNowLEA;
 206                                                                         break;
 207 #if SUPPORT_ARCH_arm64
 208                                                                 case ld::Fixup::kindStoreTargetAddressARM64GOTLoadPage21:
 209                                                                         fit->kind = ld::Fixup::kindStoreTargetAddressARM64GOTLeaPage21;
 210                                                                         break;
 211                                                                 case ld::Fixup::kindStoreTargetAddressARM64GOTLoadPageOff12:
 212                                                                         fit->kind = ld::Fixup::kindStoreTargetAddressARM64GOTLeaPageOff12;
 213                                                                         break;
 214 #endif
 215                                                                 default:
 216                                                                         assert(0 && "unsupported GOT reference kind");
 217                                                                         break;
 218                                                         }
 219                                                         break;
 220                                                 default:
 221                                                         assert(0 && "unsupported GOT reference");
 222                                                         break;
 223                                         }
 224                                 }
 225                                 else {
 226                                         // remember that we need to use GOT in this function
 227                                         if ( log ) fprintf(stderr, "found GOT use in %s to %s\n", atom->name(), targetOfGOT->name());
 228                                         if ( !atomUsesGOT ) {
 229                                                 atomsReferencingGOT.push_back(atom);
 230                                                 atomUsesGOT = true;
 231                                         }
 232                                         gotMap[targetOfGOT] = NULL;
 233                                         // record weak_import attribute
 234                                         std::map<const ld::Atom*,bool>::iterator pos = weakImportMap.find(targetOfGOT);
 235                                         if ( pos == weakImportMap.end() ) {
 236                                                 // target not in weakImportMap, so add
 237                                                 if ( log ) fprintf(stderr, "weakImportMap[%s] = %d\n", targetOfGOT->name(), targetIsWeakImport);
 238                                                 weakImportMap[targetOfGOT] = targetIsWeakImport;
 239                                         }
 240                                         else {
 241                                                 // target in weakImportMap, check for weakness mismatch
 242                                                 if ( pos->second != targetIsWeakImport ) {
 243                                                         // found mismatch
 244                                                         switch ( opts.weakReferenceMismatchTreatment() ) {
 245                                                                 case Options::kWeakReferenceMismatchError:
 246                                                                         throwf("mismatching weak references for symbol: %s", targetOfGOT->name());
 247                                                                 case Options::kWeakReferenceMismatchWeak:
 248                                                                         pos->second = true;
 249                                                                         break;
 250                                                                 case Options::kWeakReferenceMismatchNonWeak:
 251                                                                         pos->second = false;
 252                                                                         break;
 253                                                         }
 254                                                 }
 255                                         }
 256                                 }
 257                         }
 258                 }
 259         }
 260
 261         bool is64 = false;
 262         switch ( opts.architecture() ) {
 263 #if SUPPORT_ARCH_i386
 264                 case CPU_TYPE_I386:
 265                         is64 = false;
 266                         break;
 267 #endif
 268 #if SUPPORT_ARCH_x86_64
 269                 case CPU_TYPE_X86_64:
 270                         is64 = true;
 271                         break;
 272 #endif
 273 #if SUPPORT_ARCH_arm_any
 274                 case CPU_TYPE_ARM:
 275                         is64 = false;
 276                         break;
 277 #endif
 278 #if SUPPORT_ARCH_arm64
 279                 case CPU_TYPE_ARM64:
 280                         is64 = true;
 281                         break;
 282 #endif
 283         }
 284
 285         // make GOT entries
 286         for (std::map<const ld::Atom*,ld::Atom*>::iterator it = gotMap.begin(); it != gotMap.end(); ++it) {
 287                 it->second = new GOTEntryAtom(internal, it->first, weakImportMap[it->first], is64);
 288         }
 289
 290         // update atoms to use GOT entries
 291         for (std::vector<const ld::Atom*>::iterator it=atomsReferencingGOT.begin(); it != atomsReferencingGOT.end(); ++it) {
 292                 const ld::Atom* atom = *it;
 293                 const ld::Atom* targetOfGOT = NULL;
 294                 ld::Fixup::iterator fitThatSetTarget = NULL;
 295                 for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 296                         if ( fit->firstInCluster() ) {
 297                                 targetOfGOT = NULL;
 298                                 fitThatSetTarget = NULL;
 299                         }
 300                         switch ( fit->binding ) {
 301                                 case ld::Fixup::bindingsIndirectlyBound:
 302                                         targetOfGOT = internal.indirectBindingTable[fit->u.bindingIndex];
 303                                         fitThatSetTarget = fit;
 304                                         break;
 305                                 case ld::Fixup::bindingDirectlyBound:
 306                                         targetOfGOT = fit->u.target;
 307                                         fitThatSetTarget = fit;
 308                                         break;
 309                 default:
 310                     break;
 311                         }
 312                         bool optimizable;
 313                         if ( (targetOfGOT == NULL) || !gotFixup(opts, internal, targetOfGOT, fit, &optimizable) )
 314                                 continue;
 315                         if ( !optimizable ) {
 316                                 // GOT use not optimized away, update to bind to GOT entry
 317                                 assert(fitThatSetTarget != NULL);
 318                                 switch ( fitThatSetTarget->binding ) {
 319                                         case ld::Fixup::bindingsIndirectlyBound:
 320                                         case ld::Fixup::bindingDirectlyBound:
 321                                                 fitThatSetTarget->binding = ld::Fixup::bindingDirectlyBound;
 322                                                 fitThatSetTarget->u.target = gotMap[targetOfGOT];
 323                                                 break;
 324                                         default:
 325                                                 assert(0 && "unsupported GOT reference");
 326                                                 break;
 327                                 }
 328                         }
 329                 }
 330         }
 331
 332         // sort new atoms so links are consistent
 333         for (std::vector<ld::Internal::FinalSection*>::iterator sit=internal.sections.begin(); sit != internal.sections.end(); ++sit) {
 334                 ld::Internal::FinalSection* sect = *sit;
 335                 if ( sect->type() == ld::Section::typeNonLazyPointer ) {
 336                         std::sort(sect->atoms.begin(), sect->atoms.end(), AtomByNameSorter());
 337                 }
 338         }
 339 }
 340
 341
 342 } // namespace got
 343 } // namespace passes
 344 } // namespace ld