src/ld/passes/branch_island.cpp

   1 /* -*- mode: C++; c-basic-offset: 4; tab-width: 4 -*-
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   3  * Copyright (c) 2009 Apple Inc. All rights reserved.
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   7  * This file contains Original Code and/or Modifications of Original Code
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   9  * Version 2.0 (the 'License'). You may not use this file except in
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  11  * http://www.opensource.apple.com/apsl/ and read it before using this
  12  * file.
  13  *
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  24
  25
  26 #include <stdint.h>
  27 #include <math.h>
  28 #include <unistd.h>
  29 #include <dlfcn.h>
  30 #include <libkern/OSByteOrder.h>
  31
  32 #include <vector>
  33 #include <map>
  34
  35 #include "MachOFileAbstraction.hpp"
  36 #include "ld.hpp"
  37 #include "branch_island.h"
  38
  39 namespace ld {
  40 namespace passes {
  41 namespace branch_island {
  42
  43
  44
  45
  46 struct TargetAndOffset { const ld::Atom* atom; uint32_t offset; };
  47 class TargetAndOffsetComparor
  48 {
  49 public:
  50         bool operator()(const TargetAndOffset& left, const TargetAndOffset& right) const
  51         {
  52                 if ( left.atom != right.atom )
  53                         return ( left.atom < right.atom );
  54                 return ( left.offset < right.offset );
  55         }
  56 };
  57
  58
  59 static bool _s_log = false;
  60 static ld::Section _s_text_section("__TEXT", "__text", ld::Section::typeCode);
  61
  62
  63
  64 class ARMtoARMBranchIslandAtom : public ld::Atom {
  65 public:
  66                                                                                         ARMtoARMBranchIslandAtom(const char* nm, const ld::Atom* target, TargetAndOffset finalTarget)
  67                                 : ld::Atom(_s_text_section, ld::Atom::definitionRegular, ld::Atom::combineNever,
  68                                                         ld::Atom::scopeLinkageUnit, ld::Atom::typeBranchIsland,
  69                                                         ld::Atom::symbolTableIn, false, false, false, ld::Atom::Alignment(2)),
  70                                 _name(nm),
  71                                 _target(target),
  72                                 _finalTarget(finalTarget) { }
  73
  74         virtual const ld::File*                                 file() const                                    { return NULL; }
  75         virtual bool                                                    translationUnitSource(const char** dir, const char**) const
  76                                                                                                                                                         { return false; }
  77         virtual const char*                                             name() const                                    { return _name; }
  78         virtual uint64_t                                                size() const                                    { return 4; }
  79         virtual uint64_t                                                objectAddress() const                   { return 0; }
  80         virtual void                                                    copyRawContent(uint8_t buffer[]) const {
  81                 int64_t displacement = _target->finalAddress() - this->finalAddress() - 8;
  82                 if ( _target->contentType() == ld::Atom::typeBranchIsland ) {
  83                         // an ARM branch can branch farther than a thumb branch.  The branch
  84                         // island generation was conservative and put islands every thumb
  85                         // branch distance apart.  Check to see if this is a an island
  86                         // hopping branch that could be optimized to go directly to target.
  87                         int64_t skipToFinalDisplacement = _finalTarget.atom->finalAddress() + _finalTarget.offset - this->finalAddress() - 8;
  88                         if ( (skipToFinalDisplacement < 33554428LL) && (skipToFinalDisplacement > (-33554432LL)) ) {
  89                                 // can skip branch island and jump straight to target
  90                                 if (_s_log) fprintf(stderr, "%s: optimized jump to final target at 0x%08llX, thisAddr=0x%08llX\n",
  91                                                                                         _target->name(), _finalTarget.atom->finalAddress(), this->finalAddress());
  92                                 displacement = skipToFinalDisplacement;
  93                         }
  94                         else {
  95                                 // ultimate target is too far, jump to island
  96                                 if (_s_log) fprintf(stderr, "%s: jump to branch island at 0x%08llX\n",
  97                                                                                         _target->name(), _finalTarget.atom->finalAddress());
  98                         }
  99                 }
 100                 uint32_t imm24 = (displacement >> 2) & 0x00FFFFFF;
 101                 int32_t branchInstruction = 0xEA000000 | imm24;
 102                 OSWriteLittleInt32(buffer, 0, branchInstruction);
 103         }
 104         virtual void                                                    setScope(Scope)                                 { }
 105
 106 private:
 107         const char*                                                             _name;
 108         const ld::Atom*                                                 _target;
 109         TargetAndOffset                                                 _finalTarget;
 110 };
 111
 112
 113
 114 class ARMtoThumb1BranchIslandAtom : public ld::Atom {
 115 public:
 116                                                                                         ARMtoThumb1BranchIslandAtom(const char* nm, const ld::Atom* target, TargetAndOffset finalTarget)
 117                                 : ld::Atom(_s_text_section, ld::Atom::definitionRegular, ld::Atom::combineNever,
 118                                                         ld::Atom::scopeLinkageUnit, ld::Atom::typeBranchIsland,
 119                                                         ld::Atom::symbolTableIn, false, false, false, ld::Atom::Alignment(2)),
 120                                 _name(nm),
 121                                 _target(target),
 122                                 _finalTarget(finalTarget) { }
 123
 124         virtual const ld::File*                                 file() const                                    { return NULL; }
 125         virtual bool                                                    translationUnitSource(const char** dir, const char**) const
 126                                                                                                                                                         { return false; }
 127         virtual const char*                                             name() const                                    { return _name; }
 128         virtual uint64_t                                                size() const                                    { return 16; }
 129         virtual uint64_t                                                objectAddress() const                   { return 0; }
 130         virtual void                                                    copyRawContent(uint8_t buffer[]) const {
 131                 // There is no large displacement thumb1 branch instruction.
 132                 // Instead use ARM instructions that can jump to thumb.
 133                 // we use a 32-bit displacement, so we can directly jump to target which means no island hopping
 134                 int64_t displacement = _finalTarget.atom->finalAddress() + _finalTarget.offset - (this->finalAddress() + 12);
 135                 if ( _finalTarget.atom->isThumb() )
 136                         displacement |= 1;
 137                 if (_s_log) fprintf(stderr, "%s: 4 ARM instruction jump to final target at 0x%08llX\n",
 138                                                                                 _target->name(), _finalTarget.atom->finalAddress());
 139                 OSWriteLittleInt32(&buffer[ 0], 0, 0xe59fc004); //      ldr  ip, pc + 4
 140                 OSWriteLittleInt32(&buffer[ 4], 0, 0xe08fc00c); //      add      ip, pc, ip
 141                 OSWriteLittleInt32(&buffer[ 8], 0, 0xe12fff1c); //      bx       ip
 142                 OSWriteLittleInt32(&buffer[12], 0, displacement);       //      .long target-this
 143         }
 144         virtual void                                                    setScope(Scope)                                 { }
 145
 146 private:
 147         const char*                                                             _name;
 148         const ld::Atom*                                                 _target;
 149         TargetAndOffset                                                 _finalTarget;
 150 };
 151
 152
 153
 154 class Thumb2toThumbBranchIslandAtom : public ld::Atom {
 155 public:
 156                                                                                         Thumb2toThumbBranchIslandAtom(const char* nm, const ld::Atom* target, TargetAndOffset finalTarget)
 157                                 : ld::Atom(_s_text_section, ld::Atom::definitionRegular, ld::Atom::combineNever,
 158                                                         ld::Atom::scopeLinkageUnit, ld::Atom::typeBranchIsland,
 159                                                         ld::Atom::symbolTableIn, false, true, false, ld::Atom::Alignment(1)),
 160                                 _name(nm),
 161                                 _target(target),
 162                                 _finalTarget(finalTarget) { }
 163
 164         virtual const ld::File*                                 file() const                                    { return NULL; }
 165         virtual bool                                                    translationUnitSource(const char** dir, const char**) const
 166                                                                                                                                                         { return false; }
 167         virtual const char*                                             name() const                                    { return _name; }
 168         virtual uint64_t                                                size() const                                    { return 4; }
 169         virtual uint64_t                                                objectAddress() const                   { return 0; }
 170         virtual void                                                    copyRawContent(uint8_t buffer[]) const {
 171                 int64_t displacement = _target->finalAddress() - this->finalAddress() - 4;
 172                 if ( _target->contentType() == ld::Atom::typeBranchIsland ) {
 173                         // an ARM branch can branch farther than a thumb branch.  The branch
 174                         // island generation was conservative and put islands every thumb
 175                         // branch distance apart.  Check to see if this is a an island
 176                         // hopping branch that could be optimized to go directly to target.
 177                         int64_t skipToFinalDisplacement = _finalTarget.atom->finalAddress() + _finalTarget.offset - this->finalAddress() - 4;
 178                         if ( (skipToFinalDisplacement < 16777214) && (skipToFinalDisplacement > (-16777216LL)) ) {
 179                                 // can skip branch island and jump straight to target
 180                                 if (_s_log) fprintf(stderr, "%s: optimized jump to final target at 0x%08llX, thisAddr=0x%08llX\n",
 181                                                                                         _target->name(), _finalTarget.atom->finalAddress(), this->finalAddress());
 182                                 displacement = skipToFinalDisplacement;
 183                         }
 184                         else {
 185                                 // ultimate target is too far for thumb2 branch, jump to island
 186                                 if (_s_log) fprintf(stderr, "%s: jump to branch island at 0x%08llX\n",
 187                                                                                         _target->name(), _finalTarget.atom->finalAddress());
 188                         }
 189                 }
 190                 // The instruction is really two instructions:
 191                 // The lower 16 bits are the first instruction, which contains the high
 192                 //   11 bits of the displacement.
 193                 // The upper 16 bits are the second instruction, which contains the low
 194                 //   11 bits of the displacement, as well as differentiating bl and blx.
 195                 uint32_t s = (uint32_t)(displacement >> 24) & 0x1;
 196                 uint32_t i1 = (uint32_t)(displacement >> 23) & 0x1;
 197                 uint32_t i2 = (uint32_t)(displacement >> 22) & 0x1;
 198                 uint32_t imm10 = (uint32_t)(displacement >> 12) & 0x3FF;
 199                 uint32_t imm11 = (uint32_t)(displacement >> 1) & 0x7FF;
 200                 uint32_t j1 = (i1 == s);
 201                 uint32_t j2 = (i2 == s);
 202                 uint32_t opcode = 0x9000F000;
 203                 uint32_t nextDisp = (j1 << 13) | (j2 << 11) | imm11;
 204                 uint32_t firstDisp = (s << 10) | imm10;
 205                 uint32_t newInstruction = opcode | (nextDisp << 16) | firstDisp;
 206                 //warning("s=%d, j1=%d, j2=%d, imm10=0x%0X, imm11=0x%0X, opcode=0x%08X, first=0x%04X, next=0x%04X, new=0x%08X, disp=0x%llX for %s to %s\n",
 207                 //      s, j1, j2, imm10, imm11, opcode, firstDisp, nextDisp, newInstruction, displacement, inAtom->getDisplayName(), ref->getTarget().getDisplayName());
 208                 OSWriteLittleInt32(buffer, 0, newInstruction);
 209         }
 210         virtual void                                                    setScope(Scope)                                 { }
 211
 212 private:
 213         const char*                                                             _name;
 214         const ld::Atom*                                                 _target;
 215         TargetAndOffset                                                 _finalTarget;
 216 };
 217
 218
 219 class NoPicARMtoThumbMBranchIslandAtom : public ld::Atom {
 220 public:
 221                                                                                         NoPicARMtoThumbMBranchIslandAtom(const char* nm, const ld::Atom* target, TargetAndOffset finalTarget)
 222                                 : ld::Atom(_s_text_section, ld::Atom::definitionRegular, ld::Atom::combineNever,
 223                                                         ld::Atom::scopeLinkageUnit, ld::Atom::typeBranchIsland,
 224                                                         ld::Atom::symbolTableIn, false, false, false, ld::Atom::Alignment(2)),
 225                                 _name(nm),
 226                                 _target(target),
 227                                 _finalTarget(finalTarget) { }
 228
 229         virtual const ld::File*                                 file() const                                    { return NULL; }
 230         virtual bool                                                    translationUnitSource(const char** dir, const char**) const
 231                                                                                                                                                         { return false; }
 232         virtual const char*                                             name() const                                    { return _name; }
 233         virtual uint64_t                                                size() const                                    { return 8; }
 234         virtual uint64_t                                                objectAddress() const                   { return 0; }
 235         virtual void                                                    copyRawContent(uint8_t buffer[]) const {
 236                 // There is no large displacement thumb1 branch instruction.
 237                 // Instead use ARM instructions that can jump to thumb.
 238                 // we use a 32-bit displacement, so we can directly jump to final target which means no island hopping
 239                 uint32_t targetAddr = _finalTarget.atom->finalAddress();
 240                 if ( _finalTarget.atom->isThumb() )
 241                         targetAddr |= 1;
 242                 if (_s_log) fprintf(stderr, "%s: 2 ARM instruction jump to final target at 0x%08llX\n",
 243                                                                         _target->name(), _finalTarget.atom->finalAddress());
 244                 OSWriteLittleInt32(&buffer[0], 0, 0xe51ff004);  //      ldr     pc, [pc, #-4]
 245                 OSWriteLittleInt32(&buffer[4], 0, targetAddr);  //      .long target-this
 246         }
 247         virtual void                                                    setScope(Scope)                                 { }
 248
 249 private:
 250         const char*                                                             _name;
 251         const ld::Atom*                                                 _target;
 252         TargetAndOffset                                                 _finalTarget;
 253 };
 254
 255
 256 static ld::Atom* makeBranchIsland(const Options& opts, ld::Fixup::Kind kind, int islandRegion, const ld::Atom* nextTarget, TargetAndOffset finalTarget)
 257 {
 258         char* name;
 259         if ( finalTarget.offset == 0 ) {
 260                 if ( islandRegion == 0 )
 261                         asprintf(&name, "%s.island", finalTarget.atom->name());
 262                 else
 263                         asprintf(&name, "%s.island.%d", finalTarget.atom->name(), islandRegion+1);
 264         }
 265         else {
 266                 asprintf(&name, "%s_plus_%d.island.%d", finalTarget.atom->name(), finalTarget.offset, islandRegion);
 267         }
 268
 269         switch ( kind ) {
 270                 case ld::Fixup::kindStoreARMBranch24:
 271                 case ld::Fixup::kindStoreThumbBranch22:
 272                 case ld::Fixup::kindStoreTargetAddressARMBranch24:
 273                 case ld::Fixup::kindStoreTargetAddressThumbBranch22:
 274                         if ( finalTarget.atom->isThumb() ) {
 275                                 if ( opts.preferSubArchitecture() && opts.archSupportsThumb2() ) {
 276                                         return new Thumb2toThumbBranchIslandAtom(name, nextTarget, finalTarget);
 277                                 }
 278                                 else if ( opts.outputSlidable() ) {
 279                                         return new ARMtoThumb1BranchIslandAtom(name, nextTarget, finalTarget);
 280                                 }
 281                                 else {
 282                                         return new NoPicARMtoThumbMBranchIslandAtom(name, nextTarget, finalTarget);
 283                                 }
 284                         }
 285                         else {
 286                                 return new ARMtoARMBranchIslandAtom(name, nextTarget, finalTarget);
 287                         }
 288                         break;
 289                 default:
 290                         assert(0 && "unexpected branch kind");
 291                         break;
 292         }
 293         return NULL;
 294 }
 295
 296
 297 static uint64_t textSizeWhenMightNeedBranchIslands(const Options& opts, bool seenThumbBranch)
 298 {
 299         switch ( opts.architecture() ) {
 300                 case CPU_TYPE_ARM:
 301                         if ( ! seenThumbBranch )
 302                                 return 32000000;  // ARM can branch +/- 32MB
 303                         else if ( opts.preferSubArchitecture() && opts.archSupportsThumb2() )
 304                                 return 16000000;  // thumb2 can branch +/- 16MB
 305                         else
 306                                 return  4000000;  // thumb1 can branch +/- 4MB
 307                         break;
 308         }
 309         assert(0 && "unexpected architecture");
 310         return 0x100000000LL;
 311 }
 312
 313
 314 static uint64_t maxDistanceBetweenIslands(const Options& opts, bool seenThumbBranch)
 315 {
 316         switch ( opts.architecture() ) {
 317                 case CPU_TYPE_ARM:
 318                         if ( ! seenThumbBranch )
 319                                 return 30*1024*1024;    // 2MB of branch islands per 32MB
 320                         else if ( opts.preferSubArchitecture() && opts.archSupportsThumb2() )
 321                                 return 14*1024*1024;    // 2MB of branch islands per 16MB
 322                         else
 323                                 return 3500000;                 // 0.5MB of branch islands per 4MB
 324                         break;
 325         }
 326         assert(0 && "unexpected architecture");
 327         return 0x100000000LL;
 328 }
 329
 330
 331 //
 332 // PowerPC can do PC relative branches as far as +/-16MB.
 333 // If a branch target is >16MB then we insert one or more
 334 // "branch islands" between the branch and its target that
 335 // allows island hopping to the target.
 336 //
 337 // Branch Island Algorithm
 338 //
 339 // If the __TEXT segment < 16MB, then no branch islands needed
 340 // Otherwise, every 14MB into the __TEXT segment a region is
 341 // added which can contain branch islands.  Every out-of-range
 342 // bl instruction is checked.  If it crosses a region, an island
 343 // is added to that region with the same target and the bl is
 344 // adjusted to target the island instead.
 345 //
 346 // In theory, if too many islands are added to one region, it
 347 // could grow the __TEXT enough that other previously in-range
 348 // bl branches could be pushed out of range.  We reduce the
 349 // probability this could happen by placing the ranges every
 350 // 14MB which means the region would have to be 2MB (512,000 islands)
 351 // before any branches could be pushed out of range.
 352 //
 353
 354 void doPass(const Options& opts, ld::Internal& state)
 355 {
 356         // only make branch islands in final linked images
 357         if ( opts.outputKind() == Options::kObjectFile )
 358                 return;
 359
 360         // only ARM needs branch islands
 361         switch ( opts.architecture() ) {
 362                 case CPU_TYPE_ARM:
 363                         break;
 364                 default:
 365                         return;
 366         }
 367
 368         // scan to find __text section
 369         ld::Internal::FinalSection* textSection = NULL;
 370         for (std::vector<ld::Internal::FinalSection*>::iterator sit=state.sections.begin(); sit != state.sections.end(); ++sit) {
 371                 ld::Internal::FinalSection* sect = *sit;
 372                 if ( strcmp(sect->sectionName(), "__text") == 0 )
 373                         textSection = sect;
 374         }
 375         if ( textSection == NULL )
 376                 return;
 377
 378         // assign section offsets to each atom in __text section, watch for thumb branches, and find total size
 379         const bool isARM = (opts.architecture() == CPU_TYPE_ARM);
 380         bool hasThumbBranches = false;
 381         uint64_t offset = 0;
 382         for (std::vector<const ld::Atom*>::iterator ait=textSection->atoms.begin();  ait != textSection->atoms.end(); ++ait) {
 383                 const ld::Atom* atom = *ait;
 384                 // check for thumb branches
 385                 if ( isARM && ~hasThumbBranches ) {
 386                         for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 387                                 switch ( fit->kind ) {
 388                                         case ld::Fixup::kindStoreThumbBranch22:
 389                                         case ld::Fixup::kindStoreTargetAddressThumbBranch22:
 390                                                 hasThumbBranches = true;
 391                                                 break;
 392                                         default:
 393                                                 break;
 394                                 }
 395                         }
 396                 }
 397                 // align atom
 398                 ld::Atom::Alignment atomAlign = atom->alignment();
 399                 uint64_t atomAlignP2 = (1 << atomAlign.powerOf2);
 400                 uint64_t currentModulus = (offset % atomAlignP2);
 401                 if ( currentModulus != atomAlign.modulus ) {
 402                         if ( atomAlign.modulus > currentModulus )
 403                                 offset += atomAlign.modulus-currentModulus;
 404                         else
 405                                 offset += atomAlign.modulus+atomAlignP2-currentModulus;
 406                 }
 407                 (const_cast<ld::Atom*>(atom))->setSectionOffset(offset);
 408                 offset += atom->size();
 409         }
 410         uint64_t totalTextSize = offset;
 411         if ( totalTextSize < textSizeWhenMightNeedBranchIslands(opts, hasThumbBranches) )
 412                 return;
 413         if (_s_log) fprintf(stderr, "ld:  __text section size=%llu, might need branch islands\n", totalTextSize);
 414
 415         // figure out how many regions of branch islands will be needed
 416         const uint32_t kBetweenRegions = maxDistanceBetweenIslands(opts, hasThumbBranches); // place regions of islands every 14MB in __text section
 417         const int kIslandRegionsCount = totalTextSize / kBetweenRegions;
 418         typedef std::map<TargetAndOffset,const ld::Atom*, TargetAndOffsetComparor> AtomToIsland;
 419     AtomToIsland* regionsMap[kIslandRegionsCount];
 420         std::vector<const ld::Atom*>* regionsIslands[kIslandRegionsCount];
 421         for(int i=0; i < kIslandRegionsCount; ++i) {
 422                 regionsMap[i] = new AtomToIsland();
 423                 regionsIslands[i] = new std::vector<const ld::Atom*>();
 424         }
 425         unsigned int islandCount = 0;
 426         if (_s_log) fprintf(stderr, "ld: will use %u branch island regions\n", kIslandRegionsCount);
 427
 428         // create islands for branches in __text that are out of range
 429         for (std::vector<const ld::Atom*>::iterator ait=textSection->atoms.begin(); ait != textSection->atoms.end(); ++ait) {
 430                 const ld::Atom* atom = *ait;
 431                 const ld::Atom* target = NULL;
 432                 uint64_t addend = 0;
 433                 ld::Fixup* fixupWithTarget = NULL;
 434                 for (ld::Fixup::iterator fit = atom->fixupsBegin(), end=atom->fixupsEnd(); fit != end; ++fit) {
 435                         if ( fit->firstInCluster() ) {
 436                                 target = NULL;
 437                                 fixupWithTarget = NULL;
 438                                 addend = 0;
 439                         }
 440                         switch ( fit->binding ) {
 441                                 case ld::Fixup::bindingNone:
 442                                 case ld::Fixup::bindingByNameUnbound:
 443                                         break;
 444                                 case ld::Fixup::bindingByContentBound:
 445                                 case ld::Fixup::bindingDirectlyBound:
 446                                         target = fit->u.target;
 447                                         fixupWithTarget = fit;
 448                                         break;
 449                                 case ld::Fixup::bindingsIndirectlyBound:
 450                                         target = state.indirectBindingTable[fit->u.bindingIndex];
 451                                         fixupWithTarget = fit;
 452                                         break;
 453                         }
 454                         bool haveBranch = false;
 455                         switch (fit->kind) {
 456                                 case ld::Fixup::kindAddAddend:
 457                                         addend = fit->u.addend;
 458                                         break;
 459                                 case ld::Fixup::kindStoreARMBranch24:
 460                                 case ld::Fixup::kindStoreThumbBranch22:
 461                                 case ld::Fixup::kindStoreTargetAddressARMBranch24:
 462                                 case ld::Fixup::kindStoreTargetAddressThumbBranch22:
 463                                         haveBranch = true;
 464                                         break;
 465                 default:
 466                     break;
 467                         }
 468                         if ( haveBranch ) {
 469                                 int64_t srcAddr = atom->sectionOffset() + fit->offsetInAtom;
 470                                 int64_t dstAddr = target->sectionOffset() + addend;
 471                                 if ( target->section().type() == ld::Section::typeStub )
 472                                         dstAddr = totalTextSize;
 473                                 int64_t displacement = dstAddr - srcAddr;
 474                                 TargetAndOffset finalTargetAndOffset = { target, addend };
 475                                 const int64_t kBranchLimit = kBetweenRegions;
 476                                 if ( displacement > kBranchLimit ) {
 477                                         // create forward branch chain
 478                                         const ld::Atom* nextTarget = target;
 479                                         for (int i=kIslandRegionsCount-1; i >=0 ; --i) {
 480                                                 AtomToIsland* region = regionsMap[i];
 481                                                 int64_t islandRegionAddr = kBetweenRegions * (i+1);
 482                                                 if ( (srcAddr < islandRegionAddr) && (islandRegionAddr <= dstAddr) ) {
 483                                                         AtomToIsland::iterator pos = region->find(finalTargetAndOffset);
 484                                                         if ( pos == region->end() ) {
 485                                                                 ld::Atom* island = makeBranchIsland(opts, fit->kind, i, nextTarget, finalTargetAndOffset);
 486                                                                 (*region)[finalTargetAndOffset] = island;
 487                                                                 if (_s_log) fprintf(stderr, "added island %s to region %d for %s\n", island->name(), i, atom->name());
 488                                                                 regionsIslands[i]->push_back(island);
 489                                                                 ++islandCount;
 490                                                                 nextTarget = island;
 491                                                         }
 492                                                         else {
 493                                                                 nextTarget = pos->second;
 494                                                         }
 495                                                 }
 496                                         }
 497                                         if (_s_log) fprintf(stderr, "using island %s for branch to %s from %s\n", nextTarget->name(), target->name(), atom->name());
 498                                         fixupWithTarget->u.target = nextTarget;
 499                                         fixupWithTarget->binding = ld::Fixup::bindingDirectlyBound;
 500                                 }
 501                                 else if ( displacement < (-kBranchLimit) ) {
 502                                         // create back branching chain
 503                                         const ld::Atom* prevTarget = target;
 504                                         for (int i=0; i < kIslandRegionsCount ; ++i) {
 505                                                 AtomToIsland* region = regionsMap[i];
 506                                                 int64_t islandRegionAddr = kBetweenRegions * (i+1);
 507                                                 if ( (dstAddr <= islandRegionAddr) && (islandRegionAddr < srcAddr) ) {
 508                                                         AtomToIsland::iterator pos = region->find(finalTargetAndOffset);
 509                                                         if ( pos == region->end() ) {
 510                                                                 ld::Atom* island = makeBranchIsland(opts, fit->kind, i, prevTarget, finalTargetAndOffset);
 511                                                                 (*region)[finalTargetAndOffset] = island;
 512                                                                 if (_s_log) fprintf(stderr, "added back island %s to region %d for %s\n", island->name(), i, atom->name());
 513                                                                 regionsIslands[i]->push_back(island);
 514                                                                 ++islandCount;
 515                                                                 prevTarget = island;
 516                                                         }
 517                                                         else {
 518                                                                 prevTarget = pos->second;
 519                                                         }
 520                                                 }
 521                                         }
 522                                         if (_s_log) fprintf(stderr, "using back island %s for %s\n", prevTarget->name(), atom->name());
 523                                         fixupWithTarget->u.target = prevTarget;
 524                                         fixupWithTarget->binding = ld::Fixup::bindingDirectlyBound;
 525                                 }
 526                         }
 527                 }
 528         }
 529
 530
 531         // insert islands into __text section and adjust section offsets
 532         if ( islandCount > 0 ) {
 533                 if ( _s_log ) fprintf(stderr, "ld: %u branch islands required in %u regions\n", islandCount, kIslandRegionsCount);
 534                 std::vector<const ld::Atom*> newAtomList;
 535                 newAtomList.reserve(textSection->atoms.size()+islandCount);
 536                 uint64_t islandRegionAddr = kBetweenRegions;;
 537                 int regionIndex = 0;
 538                 for (std::vector<const ld::Atom*>::iterator it=textSection->atoms.begin(); it != textSection->atoms.end(); it++) {
 539                         const ld::Atom* atom = *it;
 540                         if ( (atom->sectionOffset()+atom->size()) > islandRegionAddr ) {
 541                                 std::vector<const ld::Atom*>* regionIslands = regionsIslands[regionIndex];
 542                                 for (std::vector<const ld::Atom*>::iterator rit=regionIslands->begin(); rit != regionIslands->end(); rit++) {
 543                                         const ld::Atom* islandAtom = *rit;
 544                                         newAtomList.push_back(islandAtom);
 545                                         if ( _s_log ) fprintf(stderr, "inserting island %s into __text section\n", islandAtom->name());
 546                                 }
 547                                 ++regionIndex;
 548                                 islandRegionAddr += kBetweenRegions;
 549                         }
 550                         newAtomList.push_back(atom);
 551                 }
 552                 // put any remaining islands at end of __text section
 553                 if ( regionIndex < kIslandRegionsCount ) {
 554                         std::vector<const ld::Atom*>* regionIslands = regionsIslands[regionIndex];
 555                         for (std::vector<const ld::Atom*>::iterator rit=regionIslands->begin(); rit != regionIslands->end(); rit++) {
 556                                 const ld::Atom* islandAtom = *rit;
 557                                 newAtomList.push_back(islandAtom);
 558                                 if ( _s_log ) fprintf(stderr, "inserting island %s into __text section\n", islandAtom->name());
 559                         }
 560                 }
 561                 // swap in new list of atoms for __text section
 562                 textSection->atoms.clear();
 563                 textSection->atoms = newAtomList;
 564         }
 565
 566 }
 567
 568
 569 } // namespace branch_island
 570 } // namespace passes
 571 } // namespace ld