courgette/encoded_program.cc

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "courgette/encoded_program.h"
   6
   7 #include <algorithm>
   8 #include <map>
   9 #include <string>
  10 #include <vector>
  11
  12 #include "base/environment.h"
  13 #include "base/logging.h"
  14 #include "base/memory/scoped_ptr.h"
  15 #include "base/strings/string_util.h"
  16 #include "base/strings/utf_string_conversions.h"
  17 #include "courgette/courgette.h"
  18 #include "courgette/disassembler_elf_32_arm.h"
  19 #include "courgette/streams.h"
  20 #include "courgette/types_elf.h"
  21
  22 namespace courgette {
  23
  24 // Stream indexes.
  25 const int kStreamMisc    = 0;
  26 const int kStreamOps     = 1;
  27 const int kStreamBytes   = 2;
  28 const int kStreamAbs32Indexes = 3;
  29 const int kStreamRel32Indexes = 4;
  30 const int kStreamAbs32Addresses = 5;
  31 const int kStreamRel32Addresses = 6;
  32 const int kStreamCopyCounts = 7;
  33 const int kStreamOriginAddresses = kStreamMisc;
  34
  35 const int kStreamLimit = 9;
  36
  37 // Constructor is here rather than in the header.  Although the constructor
  38 // appears to do nothing it is fact quite large because of the implicit calls to
  39 // field constructors.  Ditto for the destructor.
  40 EncodedProgram::EncodedProgram() : image_base_(0) {}
  41 EncodedProgram::~EncodedProgram() {}
  42
  43 // Serializes a vector of integral values using Varint32 coding.
  44 template<typename V>
  45 CheckBool WriteVector(const V& items, SinkStream* buffer) {
  46   size_t count = items.size();
  47   bool ok = buffer->WriteSizeVarint32(count);
  48   for (size_t i = 0; ok && i < count;  ++i) {
  49     COMPILE_ASSERT(sizeof(items[0]) <= sizeof(uint32),  // NOLINT
  50                    T_must_fit_in_uint32);
  51     ok = buffer->WriteSizeVarint32(items[i]);
  52   }
  53   return ok;
  54 }
  55
  56 template<typename V>
  57 bool ReadVector(V* items, SourceStream* buffer) {
  58   uint32 count;
  59   if (!buffer->ReadVarint32(&count))
  60     return false;
  61
  62   items->clear();
  63
  64   bool ok = items->reserve(count);
  65   for (size_t i = 0;  ok && i < count;  ++i) {
  66     uint32 item;
  67     ok = buffer->ReadVarint32(&item);
  68     if (ok)
  69       ok = items->push_back(static_cast<typename V::value_type>(item));
  70   }
  71
  72   return ok;
  73 }
  74
  75 // Serializes a vector, using delta coding followed by Varint32 coding.
  76 template<typename V>
  77 CheckBool WriteU32Delta(const V& set, SinkStream* buffer) {
  78   size_t count = set.size();
  79   bool ok = buffer->WriteSizeVarint32(count);
  80   uint32 prev = 0;
  81   for (size_t i = 0;  ok && i < count;  ++i) {
  82     uint32 current = set[i];
  83     uint32 delta = current - prev;
  84     ok = buffer->WriteVarint32(delta);
  85     prev = current;
  86   }
  87   return ok;
  88 }
  89
  90 template <typename V>
  91 static CheckBool ReadU32Delta(V* set, SourceStream* buffer) {
  92   uint32 count;
  93
  94   if (!buffer->ReadVarint32(&count))
  95     return false;
  96
  97   set->clear();
  98   bool ok = set->reserve(count);
  99   uint32 prev = 0;
 100
 101   for (size_t i = 0; ok && i < count;  ++i) {
 102     uint32 delta;
 103     ok = buffer->ReadVarint32(&delta);
 104     if (ok) {
 105       uint32 current = prev + delta;
 106       ok = set->push_back(current);
 107       prev = current;
 108     }
 109   }
 110
 111   return ok;
 112 }
 113
 114 // Write a vector as the byte representation of the contents.
 115 //
 116 // (This only really makes sense for a type T that has sizeof(T)==1, otherwise
 117 // serialized representation is not endian-agnostic.  But it is useful to keep
 118 // the possibility of a greater size for experiments comparing Varint32 encoding
 119 // of a vector of larger integrals vs a plain form.)
 120 //
 121 template<typename V>
 122 CheckBool WriteVectorU8(const V& items, SinkStream* buffer) {
 123   size_t count = items.size();
 124   bool ok = buffer->WriteSizeVarint32(count);
 125   if (count != 0 && ok) {
 126     size_t byte_count = count * sizeof(typename V::value_type);
 127     ok = buffer->Write(static_cast<const void*>(&items[0]), byte_count);
 128   }
 129   return ok;
 130 }
 131
 132 template<typename V>
 133 bool ReadVectorU8(V* items, SourceStream* buffer) {
 134   uint32 count;
 135   if (!buffer->ReadVarint32(&count))
 136     return false;
 137
 138   items->clear();
 139   bool ok = items->resize(count, 0);
 140   if (ok && count != 0) {
 141     size_t byte_count = count * sizeof(typename V::value_type);
 142     return buffer->Read(static_cast<void*>(&((*items)[0])), byte_count);
 143   }
 144   return ok;
 145 }
 146
 147 ////////////////////////////////////////////////////////////////////////////////
 148
 149 CheckBool EncodedProgram::DefineRel32Label(int index, RVA value) {
 150   return DefineLabelCommon(&rel32_rva_, index, value);
 151 }
 152
 153 CheckBool EncodedProgram::DefineAbs32Label(int index, RVA value) {
 154   return DefineLabelCommon(&abs32_rva_, index, value);
 155 }
 156
 157 static const RVA kUnassignedRVA = static_cast<RVA>(-1);
 158
 159 CheckBool EncodedProgram::DefineLabelCommon(RvaVector* rvas,
 160                                             int index,
 161                                             RVA rva) {
 162   bool ok = true;
 163   if (static_cast<int>(rvas->size()) <= index)
 164     ok = rvas->resize(index + 1, kUnassignedRVA);
 165
 166   if (ok) {
 167     DCHECK_EQ((*rvas)[index], kUnassignedRVA)
 168         << "DefineLabel double assigned " << index;
 169     (*rvas)[index] = rva;
 170   }
 171
 172   return ok;
 173 }
 174
 175 void EncodedProgram::EndLabels() {
 176   FinishLabelsCommon(&abs32_rva_);
 177   FinishLabelsCommon(&rel32_rva_);
 178 }
 179
 180 void EncodedProgram::FinishLabelsCommon(RvaVector* rvas) {
 181   // Replace all unassigned slots with the value at the previous index so they
 182   // delta-encode to zero.  (There might be better values than zero.  The way to
 183   // get that is have the higher level assembly program assign the unassigned
 184   // slots.)
 185   RVA previous = 0;
 186   size_t size = rvas->size();
 187   for (size_t i = 0;  i < size;  ++i) {
 188     if ((*rvas)[i] == kUnassignedRVA)
 189       (*rvas)[i] = previous;
 190     else
 191       previous = (*rvas)[i];
 192   }
 193 }
 194
 195 CheckBool EncodedProgram::AddOrigin(RVA origin) {
 196   return ops_.push_back(ORIGIN) && origins_.push_back(origin);
 197 }
 198
 199 CheckBool EncodedProgram::AddCopy(uint32 count, const void* bytes) {
 200   const uint8* source = static_cast<const uint8*>(bytes);
 201
 202   bool ok = true;
 203
 204   // Fold adjacent COPY instructions into one.  This nearly halves the size of
 205   // an EncodedProgram with only COPY1 instructions since there are approx plain
 206   // 16 bytes per reloc.  This has a working-set benefit during decompression.
 207   // For compression of files with large differences this makes a small (4%)
 208   // improvement in size.  For files with small differences this degrades the
 209   // compressed size by 1.3%
 210   if (!ops_.empty()) {
 211     if (ops_.back() == COPY1) {
 212       ops_.back() = COPY;
 213       ok = copy_counts_.push_back(1);
 214     }
 215     if (ok && ops_.back() == COPY) {
 216       copy_counts_.back() += count;
 217       for (uint32 i = 0; ok && i < count; ++i) {
 218         ok = copy_bytes_.push_back(source[i]);
 219       }
 220       return ok;
 221     }
 222   }
 223
 224   if (ok) {
 225     if (count == 1) {
 226       ok = ops_.push_back(COPY1) && copy_bytes_.push_back(source[0]);
 227     } else {
 228       ok = ops_.push_back(COPY) && copy_counts_.push_back(count);
 229       for (uint32 i = 0; ok && i < count; ++i) {
 230         ok = copy_bytes_.push_back(source[i]);
 231       }
 232     }
 233   }
 234
 235   return ok;
 236 }
 237
 238 CheckBool EncodedProgram::AddAbs32(int label_index) {
 239   return ops_.push_back(ABS32) && abs32_ix_.push_back(label_index);
 240 }
 241
 242 CheckBool EncodedProgram::AddRel32(int label_index) {
 243   return ops_.push_back(REL32) && rel32_ix_.push_back(label_index);
 244 }
 245
 246 CheckBool EncodedProgram::AddRel32ARM(uint16 op, int label_index) {
 247   return ops_.push_back(static_cast<OP>(op)) &&
 248       rel32_ix_.push_back(label_index);
 249 }
 250
 251 CheckBool EncodedProgram::AddPeMakeRelocs(ExecutableType kind) {
 252   if (kind == EXE_WIN_32_X86)
 253     return ops_.push_back(MAKE_PE_RELOCATION_TABLE);
 254   return ops_.push_back(MAKE_PE64_RELOCATION_TABLE);
 255 }
 256
 257 CheckBool EncodedProgram::AddElfMakeRelocs() {
 258   return ops_.push_back(MAKE_ELF_RELOCATION_TABLE);
 259 }
 260
 261 CheckBool EncodedProgram::AddElfARMMakeRelocs() {
 262   return ops_.push_back(MAKE_ELF_ARM_RELOCATION_TABLE);
 263 }
 264
 265 void EncodedProgram::DebuggingSummary() {
 266   VLOG(1) << "EncodedProgram Summary"
 267           << "\n  image base  " << image_base_
 268           << "\n  abs32 rvas  " << abs32_rva_.size()
 269           << "\n  rel32 rvas  " << rel32_rva_.size()
 270           << "\n  ops         " << ops_.size()
 271           << "\n  origins     " << origins_.size()
 272           << "\n  copy_counts " << copy_counts_.size()
 273           << "\n  copy_bytes  " << copy_bytes_.size()
 274           << "\n  abs32_ix    " << abs32_ix_.size()
 275           << "\n  rel32_ix    " << rel32_ix_.size();
 276 }
 277
 278 ////////////////////////////////////////////////////////////////////////////////
 279
 280 // For algorithm refinement purposes it is useful to write subsets of the file
 281 // format.  This gives us the ability to estimate the entropy of the
 282 // differential compression of the individual streams, which can provide
 283 // invaluable insights.  The default, of course, is to include all the streams.
 284 //
 285 enum FieldSelect {
 286   INCLUDE_ABS32_ADDRESSES = 0x0001,
 287   INCLUDE_REL32_ADDRESSES = 0x0002,
 288   INCLUDE_ABS32_INDEXES   = 0x0010,
 289   INCLUDE_REL32_INDEXES   = 0x0020,
 290   INCLUDE_OPS             = 0x0100,
 291   INCLUDE_BYTES           = 0x0200,
 292   INCLUDE_COPY_COUNTS     = 0x0400,
 293   INCLUDE_MISC            = 0x1000
 294 };
 295
 296 static FieldSelect GetFieldSelect() {
 297 #if 1
 298   // TODO(sra): Use better configuration.
 299   scoped_ptr<base::Environment> env(base::Environment::Create());
 300   std::string s;
 301   env->GetVar("A_FIELDS", &s);
 302   if (!s.empty()) {
 303     return static_cast<FieldSelect>(
 304         wcstoul(base::ASCIIToWide(s).c_str(), 0, 0));
 305   }
 306 #endif
 307   return  static_cast<FieldSelect>(~0);
 308 }
 309
 310 CheckBool EncodedProgram::WriteTo(SinkStreamSet* streams) {
 311   FieldSelect select = GetFieldSelect();
 312
 313   // The order of fields must be consistent in WriteTo and ReadFrom, regardless
 314   // of the streams used.  The code can be configured with all kStreamXXX
 315   // constants the same.
 316   //
 317   // If we change the code to pipeline reading with assembly (to avoid temporary
 318   // storage vectors by consuming operands directly from the stream) then we
 319   // need to read the base address and the random access address tables first,
 320   // the rest can be interleaved.
 321
 322   if (select & INCLUDE_MISC) {
 323     // TODO(sra): write 64 bits.
 324     if (!streams->stream(kStreamMisc)->WriteVarint32(
 325             static_cast<uint32>(image_base_))) {
 326       return false;
 327     }
 328   }
 329
 330   bool success = true;
 331
 332   if (select & INCLUDE_ABS32_ADDRESSES) {
 333     success &= WriteU32Delta(abs32_rva_,
 334                              streams->stream(kStreamAbs32Addresses));
 335   }
 336
 337   if (select & INCLUDE_REL32_ADDRESSES) {
 338     success &= WriteU32Delta(rel32_rva_,
 339                              streams->stream(kStreamRel32Addresses));
 340   }
 341
 342   if (select & INCLUDE_MISC)
 343     success &= WriteVector(origins_, streams->stream(kStreamOriginAddresses));
 344
 345   if (select & INCLUDE_OPS) {
 346     // 5 for length.
 347     success &= streams->stream(kStreamOps)->Reserve(ops_.size() + 5);
 348     success &= WriteVector(ops_, streams->stream(kStreamOps));
 349   }
 350
 351   if (select & INCLUDE_COPY_COUNTS)
 352     success &= WriteVector(copy_counts_, streams->stream(kStreamCopyCounts));
 353
 354   if (select & INCLUDE_BYTES)
 355     success &= WriteVectorU8(copy_bytes_, streams->stream(kStreamBytes));
 356
 357   if (select & INCLUDE_ABS32_INDEXES)
 358     success &= WriteVector(abs32_ix_, streams->stream(kStreamAbs32Indexes));
 359
 360   if (select & INCLUDE_REL32_INDEXES)
 361     success &= WriteVector(rel32_ix_, streams->stream(kStreamRel32Indexes));
 362
 363   return success;
 364 }
 365
 366 bool EncodedProgram::ReadFrom(SourceStreamSet* streams) {
 367   // TODO(sra): read 64 bits.
 368   uint32 temp;
 369   if (!streams->stream(kStreamMisc)->ReadVarint32(&temp))
 370     return false;
 371   image_base_ = temp;
 372
 373   if (!ReadU32Delta(&abs32_rva_, streams->stream(kStreamAbs32Addresses)))
 374     return false;
 375   if (!ReadU32Delta(&rel32_rva_, streams->stream(kStreamRel32Addresses)))
 376     return false;
 377   if (!ReadVector(&origins_, streams->stream(kStreamOriginAddresses)))
 378     return false;
 379   if (!ReadVector(&ops_, streams->stream(kStreamOps)))
 380     return false;
 381   if (!ReadVector(&copy_counts_, streams->stream(kStreamCopyCounts)))
 382     return false;
 383   if (!ReadVectorU8(&copy_bytes_, streams->stream(kStreamBytes)))
 384     return false;
 385   if (!ReadVector(&abs32_ix_, streams->stream(kStreamAbs32Indexes)))
 386     return false;
 387   if (!ReadVector(&rel32_ix_, streams->stream(kStreamRel32Indexes)))
 388     return false;
 389
 390   // Check that streams have been completely consumed.
 391   for (int i = 0;  i < kStreamLimit;  ++i) {
 392     if (streams->stream(i)->Remaining() > 0)
 393       return false;
 394   }
 395
 396   return true;
 397 }
 398
 399 // Safe, non-throwing version of std::vector::at().  Returns 'true' for success,
 400 // 'false' for out-of-bounds index error.
 401 template<typename V, typename T>
 402 bool VectorAt(const V& v, size_t index, T* output) {
 403   if (index >= v.size())
 404     return false;
 405   *output = v[index];
 406   return true;
 407 }
 408
 409 CheckBool EncodedProgram::EvaluateRel32ARM(OP op,
 410                                            size_t& ix_rel32_ix,
 411                                            RVA& current_rva,
 412                                            SinkStream* output) {
 413   switch (op & 0x0000F000) {
 414     case REL32ARM8: {
 415       uint32 index;
 416       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 417         return false;
 418       ++ix_rel32_ix;
 419       RVA rva;
 420       if (!VectorAt(rel32_rva_, index, &rva))
 421         return false;
 422       uint32 decompressed_op;
 423       if (!DisassemblerElf32ARM::Decompress(ARM_OFF8,
 424                                             static_cast<uint16>(op),
 425                                             static_cast<uint32>(rva -
 426                                                                 current_rva),
 427                                             &decompressed_op)) {
 428         return false;
 429       }
 430       uint16 op16 = decompressed_op;
 431       if (!output->Write(&op16, 2))
 432         return false;
 433       current_rva += 2;
 434       break;
 435     }
 436     case REL32ARM11: {
 437       uint32 index;
 438       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 439         return false;
 440       ++ix_rel32_ix;
 441       RVA rva;
 442       if (!VectorAt(rel32_rva_, index, &rva))
 443         return false;
 444       uint32 decompressed_op;
 445       if (!DisassemblerElf32ARM::Decompress(ARM_OFF11, (uint16) op,
 446                                             (uint32) (rva - current_rva),
 447                                             &decompressed_op)) {
 448         return false;
 449       }
 450       uint16 op16 = decompressed_op;
 451       if (!output->Write(&op16, 2))
 452         return false;
 453       current_rva += 2;
 454       break;
 455     }
 456     case REL32ARM24: {
 457       uint32 index;
 458       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 459         return false;
 460       ++ix_rel32_ix;
 461       RVA rva;
 462       if (!VectorAt(rel32_rva_, index, &rva))
 463         return false;
 464       uint32 decompressed_op;
 465       if (!DisassemblerElf32ARM::Decompress(ARM_OFF24, (uint16) op,
 466                                             (uint32) (rva - current_rva),
 467                                             &decompressed_op)) {
 468         return false;
 469       }
 470       if (!output->Write(&decompressed_op, 4))
 471         return false;
 472       current_rva += 4;
 473       break;
 474     }
 475     case REL32ARM25: {
 476       uint32 index;
 477       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 478         return false;
 479       ++ix_rel32_ix;
 480       RVA rva;
 481       if (!VectorAt(rel32_rva_, index, &rva))
 482         return false;
 483       uint32 decompressed_op;
 484       if (!DisassemblerElf32ARM::Decompress(ARM_OFF25, (uint16) op,
 485                                             (uint32) (rva - current_rva),
 486                                             &decompressed_op)) {
 487         return false;
 488       }
 489       uint32 words = (decompressed_op << 16) | (decompressed_op >> 16);
 490       if (!output->Write(&words, 4))
 491         return false;
 492       current_rva += 4;
 493       break;
 494     }
 495     case REL32ARM21: {
 496       uint32 index;
 497       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 498         return false;
 499       ++ix_rel32_ix;
 500       RVA rva;
 501       if (!VectorAt(rel32_rva_, index, &rva))
 502         return false;
 503       uint32 decompressed_op;
 504       if (!DisassemblerElf32ARM::Decompress(ARM_OFF21, (uint16) op,
 505                                             (uint32) (rva - current_rva),
 506                                             &decompressed_op)) {
 507         return false;
 508       }
 509       uint32 words = (decompressed_op << 16) | (decompressed_op >> 16);
 510       if (!output->Write(&words, 4))
 511         return false;
 512       current_rva += 4;
 513       break;
 514     }
 515     default:
 516       return false;
 517   }
 518
 519   return true;
 520 }
 521
 522 CheckBool EncodedProgram::AssembleTo(SinkStream* final_buffer) {
 523   // For the most part, the assembly process walks the various tables.
 524   // ix_mumble is the index into the mumble table.
 525   size_t ix_origins = 0;
 526   size_t ix_copy_counts = 0;
 527   size_t ix_copy_bytes = 0;
 528   size_t ix_abs32_ix = 0;
 529   size_t ix_rel32_ix = 0;
 530
 531   RVA current_rva = 0;
 532
 533   bool pending_pe_relocation_table = false;
 534   uint8 pending_pe_relocation_table_type = 0x03;  // IMAGE_REL_BASED_HIGHLOW
 535   Elf32_Word pending_elf_relocation_table_type = 0;
 536   SinkStream bytes_following_relocation_table;
 537
 538   SinkStream* output = final_buffer;
 539
 540   for (size_t ix_ops = 0;  ix_ops < ops_.size();  ++ix_ops) {
 541     OP op = ops_[ix_ops];
 542
 543     switch (op) {
 544       default:
 545         if (!EvaluateRel32ARM(op, ix_rel32_ix, current_rva, output))
 546           return false;
 547         break;
 548
 549       case ORIGIN: {
 550         RVA section_rva;
 551         if (!VectorAt(origins_, ix_origins, &section_rva))
 552           return false;
 553         ++ix_origins;
 554         current_rva = section_rva;
 555         break;
 556       }
 557
 558       case COPY: {
 559         uint32 count;
 560         if (!VectorAt(copy_counts_, ix_copy_counts, &count))
 561           return false;
 562         ++ix_copy_counts;
 563         for (uint32 i = 0;  i < count;  ++i) {
 564           uint8 b;
 565           if (!VectorAt(copy_bytes_, ix_copy_bytes, &b))
 566             return false;
 567           ++ix_copy_bytes;
 568           if (!output->Write(&b, 1))
 569             return false;
 570         }
 571         current_rva += count;
 572         break;
 573       }
 574
 575       case COPY1: {
 576         uint8 b;
 577         if (!VectorAt(copy_bytes_, ix_copy_bytes, &b))
 578           return false;
 579         ++ix_copy_bytes;
 580         if (!output->Write(&b, 1))
 581           return false;
 582         current_rva += 1;
 583         break;
 584       }
 585
 586       case REL32: {
 587         uint32 index;
 588         if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 589           return false;
 590         ++ix_rel32_ix;
 591         RVA rva;
 592         if (!VectorAt(rel32_rva_, index, &rva))
 593           return false;
 594         uint32 offset = (rva - (current_rva + 4));
 595         if (!output->Write(&offset, 4))
 596           return false;
 597         current_rva += 4;
 598         break;
 599       }
 600
 601       case ABS32: {
 602         uint32 index;
 603         if (!VectorAt(abs32_ix_, ix_abs32_ix, &index))
 604           return false;
 605         ++ix_abs32_ix;
 606         RVA rva;
 607         if (!VectorAt(abs32_rva_, index, &rva))
 608           return false;
 609         uint32 abs32 = static_cast<uint32>(rva + image_base_);
 610         if (!abs32_relocs_.push_back(current_rva) || !output->Write(&abs32, 4))
 611           return false;
 612         current_rva += 4;
 613         break;
 614       }
 615
 616       case MAKE_PE_RELOCATION_TABLE: {
 617         // We can see the base relocation anywhere, but we only have the
 618         // information to generate it at the very end.  So we divert the bytes
 619         // we are generating to a temporary stream.
 620         if (pending_pe_relocation_table)
 621           return false;  // Can't have two base relocation tables.
 622
 623         pending_pe_relocation_table = true;
 624         output = &bytes_following_relocation_table;
 625         break;
 626         // There is a potential problem *if* the instruction stream contains
 627         // some REL32 relocations following the base relocation and in the same
 628         // section.  We don't know the size of the table, so 'current_rva' will
 629         // be wrong, causing REL32 offsets to be miscalculated.  This never
 630         // happens; the base relocation table is usually in a section of its
 631         // own, a data-only section, and following everything else in the
 632         // executable except some padding zero bytes.  We could fix this by
 633         // emitting an ORIGIN after the MAKE_BASE_RELOCATION_TABLE.
 634       }
 635
 636       case MAKE_PE64_RELOCATION_TABLE: {
 637         if (pending_pe_relocation_table)
 638           return false;  // Can't have two base relocation tables.
 639
 640         pending_pe_relocation_table = true;
 641         pending_pe_relocation_table_type = 0x0A;  // IMAGE_REL_BASED_DIR64
 642         output = &bytes_following_relocation_table;
 643         break;
 644       }
 645
 646       case MAKE_ELF_ARM_RELOCATION_TABLE: {
 647         // We can see the base relocation anywhere, but we only have the
 648         // information to generate it at the very end.  So we divert the bytes
 649         // we are generating to a temporary stream.
 650         if (pending_elf_relocation_table_type)
 651           return false;  // Can't have two base relocation tables.
 652
 653         pending_elf_relocation_table_type = R_ARM_RELATIVE;
 654         output = &bytes_following_relocation_table;
 655         break;
 656       }
 657
 658       case MAKE_ELF_RELOCATION_TABLE: {
 659         // We can see the base relocation anywhere, but we only have the
 660         // information to generate it at the very end.  So we divert the bytes
 661         // we are generating to a temporary stream.
 662         if (pending_elf_relocation_table_type)
 663           return false;  // Can't have two base relocation tables.
 664
 665         pending_elf_relocation_table_type = R_386_RELATIVE;
 666         output = &bytes_following_relocation_table;
 667         break;
 668       }
 669     }
 670   }
 671
 672   if (pending_pe_relocation_table) {
 673     if (!GeneratePeRelocations(final_buffer,
 674                                pending_pe_relocation_table_type) ||
 675         !final_buffer->Append(&bytes_following_relocation_table))
 676       return false;
 677   }
 678
 679   if (pending_elf_relocation_table_type) {
 680     if (!GenerateElfRelocations(pending_elf_relocation_table_type,
 681                                 final_buffer) ||
 682         !final_buffer->Append(&bytes_following_relocation_table))
 683       return false;
 684   }
 685
 686   // Final verification check: did we consume all lists?
 687   if (ix_copy_counts != copy_counts_.size())
 688     return false;
 689   if (ix_copy_bytes != copy_bytes_.size())
 690     return false;
 691   if (ix_abs32_ix != abs32_ix_.size())
 692     return false;
 693   if (ix_rel32_ix != rel32_ix_.size())
 694     return false;
 695
 696   return true;
 697 }
 698
 699 // RelocBlock has the layout of a block of relocations in the base relocation
 700 // table file format.
 701 //
 702 struct RelocBlockPOD {
 703   uint32 page_rva;
 704   uint32 block_size;
 705   uint16 relocs[4096];  // Allow up to one relocation per byte of a 4k page.
 706 };
 707
 708 COMPILE_ASSERT(offsetof(RelocBlockPOD, relocs) == 8, reloc_block_header_size);
 709
 710 class RelocBlock {
 711  public:
 712   RelocBlock() {
 713     pod.page_rva = ~0;
 714     pod.block_size = 8;
 715   }
 716
 717   void Add(uint16 item) {
 718     pod.relocs[(pod.block_size-8)/2] = item;
 719     pod.block_size += 2;
 720   }
 721
 722   CheckBool Flush(SinkStream* buffer) WARN_UNUSED_RESULT {
 723     bool ok = true;
 724     if (pod.block_size != 8) {
 725       if (pod.block_size % 4 != 0) {  // Pad to make size multiple of 4 bytes.
 726         Add(0);
 727       }
 728       ok = buffer->Write(&pod, pod.block_size);
 729       pod.block_size = 8;
 730     }
 731     return ok;
 732   }
 733   RelocBlockPOD pod;
 734 };
 735
 736 CheckBool EncodedProgram::GeneratePeRelocations(SinkStream* buffer,
 737                                                 uint8 type) {
 738   std::sort(abs32_relocs_.begin(), abs32_relocs_.end());
 739
 740   RelocBlock block;
 741
 742   bool ok = true;
 743   for (size_t i = 0;  ok && i < abs32_relocs_.size();  ++i) {
 744     uint32 rva = abs32_relocs_[i];
 745     uint32 page_rva = rva & ~0xFFF;
 746     if (page_rva != block.pod.page_rva) {
 747       ok &= block.Flush(buffer);
 748       block.pod.page_rva = page_rva;
 749     }
 750     if (ok)
 751       block.Add(((static_cast<uint16>(type)) << 12 ) | (rva & 0xFFF));
 752   }
 753   ok &= block.Flush(buffer);
 754   return ok;
 755 }
 756
 757 CheckBool EncodedProgram::GenerateElfRelocations(Elf32_Word r_info,
 758                                                  SinkStream* buffer) {
 759   std::sort(abs32_relocs_.begin(), abs32_relocs_.end());
 760
 761   Elf32_Rel relocation_block;
 762
 763   relocation_block.r_info = r_info;
 764
 765   bool ok = true;
 766   for (size_t i = 0;  ok && i < abs32_relocs_.size();  ++i) {
 767     relocation_block.r_offset = abs32_relocs_[i];
 768     ok = buffer->Write(&relocation_block, sizeof(Elf32_Rel));
 769   }
 770
 771   return ok;
 772 }
 773 ////////////////////////////////////////////////////////////////////////////////
 774
 775 Status WriteEncodedProgram(EncodedProgram* encoded, SinkStreamSet* sink) {
 776   if (!encoded->WriteTo(sink))
 777     return C_STREAM_ERROR;
 778   return C_OK;
 779 }
 780
 781 Status ReadEncodedProgram(SourceStreamSet* streams, EncodedProgram** output) {
 782   EncodedProgram* encoded = new EncodedProgram();
 783   if (encoded->ReadFrom(streams)) {
 784     *output = encoded;
 785     return C_OK;
 786   }
 787   delete encoded;
 788   return C_DESERIALIZATION_FAILED;
 789 }
 790
 791 Status Assemble(EncodedProgram* encoded, SinkStream* buffer) {
 792   bool assembled = encoded->AssembleTo(buffer);
 793   if (assembled)
 794     return C_OK;
 795   return C_ASSEMBLY_FAILED;
 796 }
 797
 798 void DeleteEncodedProgram(EncodedProgram* encoded) {
 799   delete encoded;
 800 }
 801
 802 }  // end namespace