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() {
 252   return ops_.push_back(MAKE_PE_RELOCATION_TABLE);
 253 }
 254
 255 CheckBool EncodedProgram::AddElfMakeRelocs() {
 256   return ops_.push_back(MAKE_ELF_RELOCATION_TABLE);
 257 }
 258
 259 CheckBool EncodedProgram::AddElfARMMakeRelocs() {
 260   return ops_.push_back(MAKE_ELF_ARM_RELOCATION_TABLE);
 261 }
 262
 263 void EncodedProgram::DebuggingSummary() {
 264   VLOG(1) << "EncodedProgram Summary"
 265           << "\n  image base  " << image_base_
 266           << "\n  abs32 rvas  " << abs32_rva_.size()
 267           << "\n  rel32 rvas  " << rel32_rva_.size()
 268           << "\n  ops         " << ops_.size()
 269           << "\n  origins     " << origins_.size()
 270           << "\n  copy_counts " << copy_counts_.size()
 271           << "\n  copy_bytes  " << copy_bytes_.size()
 272           << "\n  abs32_ix    " << abs32_ix_.size()
 273           << "\n  rel32_ix    " << rel32_ix_.size();
 274 }
 275
 276 ////////////////////////////////////////////////////////////////////////////////
 277
 278 // For algorithm refinement purposes it is useful to write subsets of the file
 279 // format.  This gives us the ability to estimate the entropy of the
 280 // differential compression of the individual streams, which can provide
 281 // invaluable insights.  The default, of course, is to include all the streams.
 282 //
 283 enum FieldSelect {
 284   INCLUDE_ABS32_ADDRESSES = 0x0001,
 285   INCLUDE_REL32_ADDRESSES = 0x0002,
 286   INCLUDE_ABS32_INDEXES   = 0x0010,
 287   INCLUDE_REL32_INDEXES   = 0x0020,
 288   INCLUDE_OPS             = 0x0100,
 289   INCLUDE_BYTES           = 0x0200,
 290   INCLUDE_COPY_COUNTS     = 0x0400,
 291   INCLUDE_MISC            = 0x1000
 292 };
 293
 294 static FieldSelect GetFieldSelect() {
 295 #if 1
 296   // TODO(sra): Use better configuration.
 297   scoped_ptr<base::Environment> env(base::Environment::Create());
 298   std::string s;
 299   env->GetVar("A_FIELDS", &s);
 300   if (!s.empty()) {
 301     return static_cast<FieldSelect>(wcstoul(ASCIIToWide(s).c_str(), 0, 0));
 302   }
 303 #endif
 304   return  static_cast<FieldSelect>(~0);
 305 }
 306
 307 CheckBool EncodedProgram::WriteTo(SinkStreamSet* streams) {
 308   FieldSelect select = GetFieldSelect();
 309
 310   // The order of fields must be consistent in WriteTo and ReadFrom, regardless
 311   // of the streams used.  The code can be configured with all kStreamXXX
 312   // constants the same.
 313   //
 314   // If we change the code to pipeline reading with assembly (to avoid temporary
 315   // storage vectors by consuming operands directly from the stream) then we
 316   // need to read the base address and the random access address tables first,
 317   // the rest can be interleaved.
 318
 319   if (select & INCLUDE_MISC) {
 320     // TODO(sra): write 64 bits.
 321     if (!streams->stream(kStreamMisc)->WriteVarint32(
 322             static_cast<uint32>(image_base_))) {
 323       return false;
 324     }
 325   }
 326
 327   bool success = true;
 328
 329   if (select & INCLUDE_ABS32_ADDRESSES) {
 330     success &= WriteU32Delta(abs32_rva_,
 331                              streams->stream(kStreamAbs32Addresses));
 332   }
 333
 334   if (select & INCLUDE_REL32_ADDRESSES) {
 335     success &= WriteU32Delta(rel32_rva_,
 336                              streams->stream(kStreamRel32Addresses));
 337   }
 338
 339   if (select & INCLUDE_MISC)
 340     success &= WriteVector(origins_, streams->stream(kStreamOriginAddresses));
 341
 342   if (select & INCLUDE_OPS) {
 343     // 5 for length.
 344     success &= streams->stream(kStreamOps)->Reserve(ops_.size() + 5);
 345     success &= WriteVector(ops_, streams->stream(kStreamOps));
 346   }
 347
 348   if (select & INCLUDE_COPY_COUNTS)
 349     success &= WriteVector(copy_counts_, streams->stream(kStreamCopyCounts));
 350
 351   if (select & INCLUDE_BYTES)
 352     success &= WriteVectorU8(copy_bytes_, streams->stream(kStreamBytes));
 353
 354   if (select & INCLUDE_ABS32_INDEXES)
 355     success &= WriteVector(abs32_ix_, streams->stream(kStreamAbs32Indexes));
 356
 357   if (select & INCLUDE_REL32_INDEXES)
 358     success &= WriteVector(rel32_ix_, streams->stream(kStreamRel32Indexes));
 359
 360   return success;
 361 }
 362
 363 bool EncodedProgram::ReadFrom(SourceStreamSet* streams) {
 364   // TODO(sra): read 64 bits.
 365   uint32 temp;
 366   if (!streams->stream(kStreamMisc)->ReadVarint32(&temp))
 367     return false;
 368   image_base_ = temp;
 369
 370   if (!ReadU32Delta(&abs32_rva_, streams->stream(kStreamAbs32Addresses)))
 371     return false;
 372   if (!ReadU32Delta(&rel32_rva_, streams->stream(kStreamRel32Addresses)))
 373     return false;
 374   if (!ReadVector(&origins_, streams->stream(kStreamOriginAddresses)))
 375     return false;
 376   if (!ReadVector(&ops_, streams->stream(kStreamOps)))
 377     return false;
 378   if (!ReadVector(&copy_counts_, streams->stream(kStreamCopyCounts)))
 379     return false;
 380   if (!ReadVectorU8(&copy_bytes_, streams->stream(kStreamBytes)))
 381     return false;
 382   if (!ReadVector(&abs32_ix_, streams->stream(kStreamAbs32Indexes)))
 383     return false;
 384   if (!ReadVector(&rel32_ix_, streams->stream(kStreamRel32Indexes)))
 385     return false;
 386
 387   // Check that streams have been completely consumed.
 388   for (int i = 0;  i < kStreamLimit;  ++i) {
 389     if (streams->stream(i)->Remaining() > 0)
 390       return false;
 391   }
 392
 393   return true;
 394 }
 395
 396 // Safe, non-throwing version of std::vector::at().  Returns 'true' for success,
 397 // 'false' for out-of-bounds index error.
 398 template<typename V, typename T>
 399 bool VectorAt(const V& v, size_t index, T* output) {
 400   if (index >= v.size())
 401     return false;
 402   *output = v[index];
 403   return true;
 404 }
 405
 406 CheckBool EncodedProgram::EvaluateRel32ARM(OP op,
 407                                            size_t& ix_rel32_ix,
 408                                            RVA& current_rva,
 409                                            SinkStream* output) {
 410   switch (op & 0x0000F000) {
 411     case REL32ARM8: {
 412       uint32 index;
 413       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 414         return false;
 415       ++ix_rel32_ix;
 416       RVA rva;
 417       if (!VectorAt(rel32_rva_, index, &rva))
 418         return false;
 419       uint32 decompressed_op;
 420       if (!DisassemblerElf32ARM::Decompress(ARM_OFF8,
 421                                             static_cast<uint16>(op),
 422                                             static_cast<uint32>(rva -
 423                                                                 current_rva),
 424                                             &decompressed_op)) {
 425         return false;
 426       }
 427       uint16 op16 = decompressed_op;
 428       if (!output->Write(&op16, 2))
 429         return false;
 430       current_rva += 2;
 431       break;
 432     }
 433     case REL32ARM11: {
 434       uint32 index;
 435       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 436         return false;
 437       ++ix_rel32_ix;
 438       RVA rva;
 439       if (!VectorAt(rel32_rva_, index, &rva))
 440         return false;
 441       uint32 decompressed_op;
 442       if (!DisassemblerElf32ARM::Decompress(ARM_OFF11, (uint16) op,
 443                                             (uint32) (rva - current_rva),
 444                                             &decompressed_op)) {
 445         return false;
 446       }
 447       uint16 op16 = decompressed_op;
 448       if (!output->Write(&op16, 2))
 449         return false;
 450       current_rva += 2;
 451       break;
 452     }
 453     case REL32ARM24: {
 454       uint32 index;
 455       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 456         return false;
 457       ++ix_rel32_ix;
 458       RVA rva;
 459       if (!VectorAt(rel32_rva_, index, &rva))
 460         return false;
 461       uint32 decompressed_op;
 462       if (!DisassemblerElf32ARM::Decompress(ARM_OFF24, (uint16) op,
 463                                             (uint32) (rva - current_rva),
 464                                             &decompressed_op)) {
 465         return false;
 466       }
 467       if (!output->Write(&decompressed_op, 4))
 468         return false;
 469       current_rva += 4;
 470       break;
 471     }
 472     case REL32ARM25: {
 473       uint32 index;
 474       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 475         return false;
 476       ++ix_rel32_ix;
 477       RVA rva;
 478       if (!VectorAt(rel32_rva_, index, &rva))
 479         return false;
 480       uint32 decompressed_op;
 481       if (!DisassemblerElf32ARM::Decompress(ARM_OFF25, (uint16) op,
 482                                             (uint32) (rva - current_rva),
 483                                             &decompressed_op)) {
 484         return false;
 485       }
 486       uint32 words = (decompressed_op << 16) | (decompressed_op >> 16);
 487       if (!output->Write(&words, 4))
 488         return false;
 489       current_rva += 4;
 490       break;
 491     }
 492     case REL32ARM21: {
 493       uint32 index;
 494       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 495         return false;
 496       ++ix_rel32_ix;
 497       RVA rva;
 498       if (!VectorAt(rel32_rva_, index, &rva))
 499         return false;
 500       uint32 decompressed_op;
 501       if (!DisassemblerElf32ARM::Decompress(ARM_OFF21, (uint16) op,
 502                                             (uint32) (rva - current_rva),
 503                                             &decompressed_op)) {
 504         return false;
 505       }
 506       uint32 words = (decompressed_op << 16) | (decompressed_op >> 16);
 507       if (!output->Write(&words, 4))
 508         return false;
 509       current_rva += 4;
 510       break;
 511     }
 512     default:
 513       return false;
 514   }
 515
 516   return true;
 517 }
 518
 519 CheckBool EncodedProgram::AssembleTo(SinkStream* final_buffer) {
 520   // For the most part, the assembly process walks the various tables.
 521   // ix_mumble is the index into the mumble table.
 522   size_t ix_origins = 0;
 523   size_t ix_copy_counts = 0;
 524   size_t ix_copy_bytes = 0;
 525   size_t ix_abs32_ix = 0;
 526   size_t ix_rel32_ix = 0;
 527
 528   RVA current_rva = 0;
 529
 530   bool pending_pe_relocation_table = false;
 531   Elf32_Word pending_elf_relocation_table_type = 0;
 532   SinkStream bytes_following_relocation_table;
 533
 534   SinkStream* output = final_buffer;
 535
 536   for (size_t ix_ops = 0;  ix_ops < ops_.size();  ++ix_ops) {
 537     OP op = ops_[ix_ops];
 538
 539     switch (op) {
 540       default:
 541         if (!EvaluateRel32ARM(op, ix_rel32_ix, current_rva, output))
 542           return false;
 543         break;
 544
 545       case ORIGIN: {
 546         RVA section_rva;
 547         if (!VectorAt(origins_, ix_origins, &section_rva))
 548           return false;
 549         ++ix_origins;
 550         current_rva = section_rva;
 551         break;
 552       }
 553
 554       case COPY: {
 555         uint32 count;
 556         if (!VectorAt(copy_counts_, ix_copy_counts, &count))
 557           return false;
 558         ++ix_copy_counts;
 559         for (uint32 i = 0;  i < count;  ++i) {
 560           uint8 b;
 561           if (!VectorAt(copy_bytes_, ix_copy_bytes, &b))
 562             return false;
 563           ++ix_copy_bytes;
 564           if (!output->Write(&b, 1))
 565             return false;
 566         }
 567         current_rva += count;
 568         break;
 569       }
 570
 571       case COPY1: {
 572         uint8 b;
 573         if (!VectorAt(copy_bytes_, ix_copy_bytes, &b))
 574           return false;
 575         ++ix_copy_bytes;
 576         if (!output->Write(&b, 1))
 577           return false;
 578         current_rva += 1;
 579         break;
 580       }
 581
 582       case REL32: {
 583         uint32 index;
 584         if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 585           return false;
 586         ++ix_rel32_ix;
 587         RVA rva;
 588         if (!VectorAt(rel32_rva_, index, &rva))
 589           return false;
 590         uint32 offset = (rva - (current_rva + 4));
 591         if (!output->Write(&offset, 4))
 592           return false;
 593         current_rva += 4;
 594         break;
 595       }
 596
 597       case ABS32: {
 598         uint32 index;
 599         if (!VectorAt(abs32_ix_, ix_abs32_ix, &index))
 600           return false;
 601         ++ix_abs32_ix;
 602         RVA rva;
 603         if (!VectorAt(abs32_rva_, index, &rva))
 604           return false;
 605         uint32 abs32 = static_cast<uint32>(rva + image_base_);
 606         if (!abs32_relocs_.push_back(current_rva) || !output->Write(&abs32, 4))
 607           return false;
 608         current_rva += 4;
 609         break;
 610       }
 611
 612       case MAKE_PE_RELOCATION_TABLE: {
 613         // We can see the base relocation anywhere, but we only have the
 614         // information to generate it at the very end.  So we divert the bytes
 615         // we are generating to a temporary stream.
 616         if (pending_pe_relocation_table)  // Can't have two base relocation
 617                                             // tables.
 618           return false;
 619
 620         pending_pe_relocation_table = true;
 621         output = &bytes_following_relocation_table;
 622         break;
 623         // There is a potential problem *if* the instruction stream contains
 624         // some REL32 relocations following the base relocation and in the same
 625         // section.  We don't know the size of the table, so 'current_rva' will
 626         // be wrong, causing REL32 offsets to be miscalculated.  This never
 627         // happens; the base relocation table is usually in a section of its
 628         // own, a data-only section, and following everything else in the
 629         // executable except some padding zero bytes.  We could fix this by
 630         // emitting an ORIGIN after the MAKE_BASE_RELOCATION_TABLE.
 631       }
 632
 633       case MAKE_ELF_ARM_RELOCATION_TABLE: {
 634         // We can see the base relocation anywhere, but we only have the
 635         // information to generate it at the very end.  So we divert the bytes
 636         // we are generating to a temporary stream.
 637         if (pending_elf_relocation_table_type)  // Can't have two relocation
 638                                                 // tables.
 639           return false;
 640
 641         pending_elf_relocation_table_type = R_ARM_RELATIVE;
 642         output = &bytes_following_relocation_table;
 643         break;
 644       }
 645
 646       case MAKE_ELF_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)  // Can't have two relocation
 651                                                 // tables.
 652           return false;
 653
 654         pending_elf_relocation_table_type = R_386_RELATIVE;
 655         output = &bytes_following_relocation_table;
 656         break;
 657       }
 658     }
 659   }
 660
 661   if (pending_pe_relocation_table) {
 662     if (!GeneratePeRelocations(final_buffer) ||
 663         !final_buffer->Append(&bytes_following_relocation_table))
 664       return false;
 665   }
 666
 667   if (pending_elf_relocation_table_type) {
 668     if (!GenerateElfRelocations(pending_elf_relocation_table_type,
 669                                 final_buffer) ||
 670         !final_buffer->Append(&bytes_following_relocation_table))
 671       return false;
 672   }
 673
 674   // Final verification check: did we consume all lists?
 675   if (ix_copy_counts != copy_counts_.size())
 676     return false;
 677   if (ix_copy_bytes != copy_bytes_.size())
 678     return false;
 679   if (ix_abs32_ix != abs32_ix_.size())
 680     return false;
 681   if (ix_rel32_ix != rel32_ix_.size())
 682     return false;
 683
 684   return true;
 685 }
 686
 687 // RelocBlock has the layout of a block of relocations in the base relocation
 688 // table file format.
 689 //
 690 struct RelocBlockPOD {
 691   uint32 page_rva;
 692   uint32 block_size;
 693   uint16 relocs[4096];  // Allow up to one relocation per byte of a 4k page.
 694 };
 695
 696 COMPILE_ASSERT(offsetof(RelocBlockPOD, relocs) == 8, reloc_block_header_size);
 697
 698 class RelocBlock {
 699  public:
 700   RelocBlock() {
 701     pod.page_rva = ~0;
 702     pod.block_size = 8;
 703   }
 704
 705   void Add(uint16 item) {
 706     pod.relocs[(pod.block_size-8)/2] = item;
 707     pod.block_size += 2;
 708   }
 709
 710   CheckBool Flush(SinkStream* buffer) WARN_UNUSED_RESULT {
 711     bool ok = true;
 712     if (pod.block_size != 8) {
 713       if (pod.block_size % 4 != 0) {  // Pad to make size multiple of 4 bytes.
 714         Add(0);
 715       }
 716       ok = buffer->Write(&pod, pod.block_size);
 717       pod.block_size = 8;
 718     }
 719     return ok;
 720   }
 721   RelocBlockPOD pod;
 722 };
 723
 724 CheckBool EncodedProgram::GeneratePeRelocations(SinkStream* buffer) {
 725   std::sort(abs32_relocs_.begin(), abs32_relocs_.end());
 726
 727   RelocBlock block;
 728
 729   bool ok = true;
 730   for (size_t i = 0;  ok && i < abs32_relocs_.size();  ++i) {
 731     uint32 rva = abs32_relocs_[i];
 732     uint32 page_rva = rva & ~0xFFF;
 733     if (page_rva != block.pod.page_rva) {
 734       ok &= block.Flush(buffer);
 735       block.pod.page_rva = page_rva;
 736     }
 737     if (ok)
 738       block.Add(0x3000 | (rva & 0xFFF));
 739   }
 740   ok &= block.Flush(buffer);
 741   return ok;
 742 }
 743
 744 CheckBool EncodedProgram::GenerateElfRelocations(Elf32_Word r_info,
 745                                                  SinkStream* buffer) {
 746   std::sort(abs32_relocs_.begin(), abs32_relocs_.end());
 747
 748   Elf32_Rel relocation_block;
 749
 750   relocation_block.r_info = r_info;
 751
 752   bool ok = true;
 753   for (size_t i = 0;  ok && i < abs32_relocs_.size();  ++i) {
 754     relocation_block.r_offset = abs32_relocs_[i];
 755     ok = buffer->Write(&relocation_block, sizeof(Elf32_Rel));
 756   }
 757
 758   return ok;
 759 }
 760 ////////////////////////////////////////////////////////////////////////////////
 761
 762 Status WriteEncodedProgram(EncodedProgram* encoded, SinkStreamSet* sink) {
 763   if (!encoded->WriteTo(sink))
 764     return C_STREAM_ERROR;
 765   return C_OK;
 766 }
 767
 768 Status ReadEncodedProgram(SourceStreamSet* streams, EncodedProgram** output) {
 769   EncodedProgram* encoded = new EncodedProgram();
 770   if (encoded->ReadFrom(streams)) {
 771     *output = encoded;
 772     return C_OK;
 773   }
 774   delete encoded;
 775   return C_DESERIALIZATION_FAILED;
 776 }
 777
 778 Status Assemble(EncodedProgram* encoded, SinkStream* buffer) {
 779   bool assembled = encoded->AssembleTo(buffer);
 780   if (assembled)
 781     return C_OK;
 782   return C_ASSEMBLY_FAILED;
 783 }
 784
 785 void DeleteEncodedProgram(EncodedProgram* encoded) {
 786   delete encoded;
 787 }
 788
 789 }  // end namespace