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 #include <ext/hash_map>
  34
  35 #include "ld.hpp"
  36 #include "got.h"
  37
  38 namespace ld {
  39 namespace passes {
  40 namespace got {
  41
  42 class File; // forward reference
  43
  44 class GOTEntryAtom : public ld::Atom {
  45 public:
  46                                                                                         GOTEntryAtom(ld::Internal& internal, const ld::Atom* target, bool weakImport)
  47                                 : ld::Atom(_s_section, ld::Atom::definitionRegular, ld::Atom::combineNever,
  48                                                         ld::Atom::scopeLinkageUnit, ld::Atom::typeNonLazyPointer,
  49                                                         symbolTableNotIn, false, false, false, ld::Atom::Alignment(3)),
  50                                 _fixup(0, ld::Fixup::k1of1, ld::Fixup::kindStoreTargetAddressLittleEndian64, target),
  51                                 _target(target)
  52                                         { _fixup.weakImport = weakImport; internal.addAtom(*this); }
  53
  54         virtual const ld::File*                                 file() const                                    { return NULL; }
  55         virtual const char*                                             name() const                                    { return _target->name(); }
  56         virtual uint64_t                                                size() const                                    { return 8; }
  57         virtual uint64_t                                                objectAddress() const                   { return 0; }
  58         virtual void                                                    copyRawContent(uint8_t buffer[]) const { }
  59         virtual void                                                    setScope(Scope)                                 { }
  60         virtual ld::Fixup::iterator                             fixupsBegin() const                             { return &_fixup; }
  61         virtual ld::Fixup::iterator                             fixupsEnd()     const                           { return &((ld::Fixup*)&_fixup)[1]; }
  62
  63 private:
  64         mutable ld::Fixup                                               _fixup;
  65         const ld::Atom*                                                 _target;
  66
  67         static ld::Section                                              _s_section;
  68 };
  69
  70 ld::Section GOTEntryAtom::_s_section("__DATA", "__got", ld::Section::typeNonLazyPointer);
  71
  72
  73 static bool gotFixup(const Options& opts, ld::Internal& internal, const ld::Atom* targetOfGOT, const ld::Fixup* fixup, bool* optimizable)
  74 {
  75         switch (fixup->kind) {
  76                 case ld::Fixup::kindStoreTargetAddressX86PCRel32GOTLoad:
  77                         // start by assuming this can be optimized
  78                         *optimizable = true;
  79                         // cannot do LEA optimization if target is in another dylib
  80                         if ( targetOfGOT->definition() == ld::Atom::definitionProxy )
  81                                 *optimizable = false;
  82                         // cannot do LEA optimization if target in __huge section
  83                         if ( internal.usingHugeSections && (targetOfGOT->size() > 1024*1024)
  84                                                                                         && (   (targetOfGOT->section().type() == ld::Section::typeZeroFill)
  85                                                                                                 || (targetOfGOT->section().type() == ld::Section::typeTentativeDefs)) ) {
  86                                 *optimizable = false;
  87                         }
  88                         if ( targetOfGOT->scope() == ld::Atom::scopeGlobal ) {
  89                                 // cannot do LEA optimization if target is weak exported symbol
  90                                 if ( (targetOfGOT->definition() == ld::Atom::definitionRegular) && (targetOfGOT->combine() == ld::Atom::combineByName) ) {
  91                                         switch ( opts.outputKind() ) {
  92                                                 case Options::kDynamicExecutable:
  93                                                 case Options::kDynamicLibrary:
  94                                                 case Options::kDynamicBundle:
  95                                                 case Options::kKextBundle:
  96                                                         *optimizable = false;
  97                                                         break;
  98                                                 case Options::kStaticExecutable:
  99                                                 case Options::kDyld:
 100                                                 case Options::kPreload:
 101                                                 case Options::kObjectFile:
 102                                                         break;
 103                                         }
 104                                 }
 105                                 // cannot do LEA optimization if target is interposable
 106                                 if ( opts.interposable(targetOfGOT->name()) )
 107                                         *optimizable = false;
 108                                 // cannot do LEA optimization if target is resolver function
 109                                 if ( targetOfGOT->contentType() == ld::Atom::typeResolver )
 110                                         *optimizable = false;
 111                                 // cannot do LEA optimization for flat-namespace
 112                                 if ( opts.nameSpace() != Options::kTwoLevelNameSpace )
 113                                         *optimizable = false;
 114                         }
 115                         return true;
 116                 case ld::Fixup::kindStoreX86PCRel32GOT:
 117                         *optimizable = false;
 118                         return true;
 119                 case ld::Fixup::kindNoneGroupSubordinatePersonality:
 120                         *optimizable = false;
 121                         return true;
 122                 default:
 123                         break;
 124         }
 125
 126         return false;
 127 }
 128
 129 struct AtomByNameSorter
 130 {
 131          bool operator()(const ld::Atom* left, const ld::Atom* right)
 132          {
 133                   return (strcmp(left->name(), right->name()) < 0);
 134          }
 135 };
 136
 137 void doPass(const Options& opts, ld::Internal& internal)
 138 {
 139         const bool log = false;
 140
 141         // only make got section in final linked images
 142         if ( opts.outputKind() == Options::kObjectFile )
 143                 return;
 144
 145         // walk all atoms and fixups looking for GOT-able references
 146         // don't create GOT atoms during this loop because that could invalidate the sections iterator
 147         std::vector<const ld::Atom*> atomsReferencingGOT;
 148         std::map<const ld::Atom*,ld::Atom*> gotMap;
 149         std::map<const ld::Atom*,bool>          weakImportMap;
 150         atomsReferencingGOT.reserve(128);
 151         for (std::vector<ld::Internal::FinalSection*>::iterator sit=internal.sections.begin(); sit != internal.sections.end(); ++sit) {
 152                 ld::Internal::FinalSection* sect = *sit;
 153                 for (std::vector<const ld::Atom*>::iterator ait=sect->atoms.begin();  ait != sect->atoms.end(); ++ait) {
 154                         const ld::Atom* atom = *ait;
 155                         bool atomUsesGOT = false;
 156                         const ld::Atom* targetOfGOT = NULL;
 157                         bool targetIsWeakImport = false;
 158                         for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 159                                 if ( fit->firstInCluster() )
 160                                         targetOfGOT = NULL;
 161                                 switch ( fit->binding ) {
 162                                         case ld::Fixup::bindingsIndirectlyBound:
 163                                                 targetOfGOT = internal.indirectBindingTable[fit->u.bindingIndex];
 164                                                 targetIsWeakImport = fit->weakImport;
 165                                                 break;
 166                                         case ld::Fixup::bindingDirectlyBound:
 167                                                 targetOfGOT = fit->u.target;
 168                                                 targetIsWeakImport = fit->weakImport;
 169                                                 break;
 170                     default:
 171                         break;
 172                                 }
 173                                 bool optimizable;
 174                                 if ( !gotFixup(opts, internal, targetOfGOT, fit, &optimizable) )
 175                                         continue;
 176                                 if ( optimizable ) {
 177                                         // change from load of GOT entry to lea of target
 178                                         if ( log ) fprintf(stderr, "optimized GOT usage in %s to %s\n", atom->name(), targetOfGOT->name());
 179                                         switch ( fit->binding ) {
 180                                                 case ld::Fixup::bindingsIndirectlyBound:
 181                                                 case ld::Fixup::bindingDirectlyBound:
 182                                                         fit->binding = ld::Fixup::bindingDirectlyBound;
 183                                                         fit->u.target = targetOfGOT;
 184                                                         fit->kind = ld::Fixup::kindStoreTargetAddressX86PCRel32GOTLoadNowLEA;
 185                                                         break;
 186                                                 default:
 187                                                         assert(0 && "unsupported GOT reference");
 188                                                         break;
 189                                         }
 190                                 }
 191                                 else {
 192                                         // remember that we need to use GOT in this function
 193                                         if ( log ) fprintf(stderr, "found GOT use in %s to %s\n", atom->name(), targetOfGOT->name());
 194                                         if ( !atomUsesGOT ) {
 195                                                 atomsReferencingGOT.push_back(atom);
 196                                                 atomUsesGOT = true;
 197                                         }
 198                                         gotMap[targetOfGOT] = NULL;
 199                                         // record weak_import attribute
 200                                         std::map<const ld::Atom*,bool>::iterator pos = weakImportMap.find(targetOfGOT);
 201                                         if ( pos == weakImportMap.end() ) {
 202                                                 // target not in weakImportMap, so add
 203                                                 if ( log ) fprintf(stderr, "weakImportMap[%s] = %d\n", targetOfGOT->name(), targetIsWeakImport);
 204                                                 weakImportMap[targetOfGOT] = targetIsWeakImport;
 205                                         }
 206                                         else {
 207                                                 // target in weakImportMap, check for weakness mismatch
 208                                                 if ( pos->second != targetIsWeakImport ) {
 209                                                         // found mismatch
 210                                                         switch ( opts.weakReferenceMismatchTreatment() ) {
 211                                                                 case Options::kWeakReferenceMismatchError:
 212                                                                         throwf("mismatching weak references for symbol: %s", targetOfGOT->name());
 213                                                                 case Options::kWeakReferenceMismatchWeak:
 214                                                                         pos->second = true;
 215                                                                         break;
 216                                                                 case Options::kWeakReferenceMismatchNonWeak:
 217                                                                         pos->second = false;
 218                                                                         break;
 219                                                         }
 220                                                 }
 221                                         }
 222                                 }
 223                         }
 224                 }
 225         }
 226
 227         // make GOT entries
 228         for (std::map<const ld::Atom*,ld::Atom*>::iterator it = gotMap.begin(); it != gotMap.end(); ++it) {
 229                 it->second = new GOTEntryAtom(internal, it->first, weakImportMap[it->first]);
 230         }
 231
 232         // update atoms to use GOT entries
 233         for (std::vector<const ld::Atom*>::iterator it=atomsReferencingGOT.begin(); it != atomsReferencingGOT.end(); ++it) {
 234                 const ld::Atom* atom = *it;
 235                 const ld::Atom* targetOfGOT = NULL;
 236                 ld::Fixup::iterator fitThatSetTarget = NULL;
 237                 for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 238                         if ( fit->firstInCluster() ) {
 239                                 targetOfGOT = NULL;
 240                                 fitThatSetTarget = NULL;
 241                         }
 242                         switch ( fit->binding ) {
 243                                 case ld::Fixup::bindingsIndirectlyBound:
 244                                         targetOfGOT = internal.indirectBindingTable[fit->u.bindingIndex];
 245                                         fitThatSetTarget = fit;
 246                                         break;
 247                                 case ld::Fixup::bindingDirectlyBound:
 248                                         targetOfGOT = fit->u.target;
 249                                         fitThatSetTarget = fit;
 250                                         break;
 251                 default:
 252                     break;
 253                         }
 254                         bool optimizable;
 255                         if ( (targetOfGOT == NULL) || !gotFixup(opts, internal, targetOfGOT, fit, &optimizable) )
 256                                 continue;
 257                         if ( !optimizable ) {
 258                                 // GOT use not optimized away, update to bind to GOT entry
 259                                 assert(fitThatSetTarget != NULL);
 260                                 switch ( fitThatSetTarget->binding ) {
 261                                         case ld::Fixup::bindingsIndirectlyBound:
 262                                         case ld::Fixup::bindingDirectlyBound:
 263                                                 fitThatSetTarget->binding = ld::Fixup::bindingDirectlyBound;
 264                                                 fitThatSetTarget->u.target = gotMap[targetOfGOT];
 265                                                 break;
 266                                         default:
 267                                                 assert(0 && "unsupported GOT reference");
 268                                                 break;
 269                                 }
 270                         }
 271                 }
 272         }
 273
 274         // sort new atoms so links are consistent
 275         for (std::vector<ld::Internal::FinalSection*>::iterator sit=internal.sections.begin(); sit != internal.sections.end(); ++sit) {
 276                 ld::Internal::FinalSection* sect = *sit;
 277                 if ( sect->type() == ld::Section::typeNonLazyPointer ) {
 278                         std::sort(sect->atoms.begin(), sect->atoms.end(), AtomByNameSorter());
 279                 }
 280         }
 281 }
 282
 283
 284 } // namespace got
 285 } // namespace passes
 286 } // namespace ld