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_number_conversions.h"
  16 #include "base/strings/string_util.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     ok = buffer->WriteSizeVarint32(items[i]);
  50   }
  51   return ok;
  52 }
  53
  54 template<typename V>
  55 bool ReadVector(V* items, SourceStream* buffer) {
  56   uint32 count;
  57   if (!buffer->ReadVarint32(&count))
  58     return false;
  59
  60   items->clear();
  61
  62   bool ok = items->reserve(count);
  63   for (size_t i = 0;  ok && i < count;  ++i) {
  64     uint32 item;
  65     ok = buffer->ReadVarint32(&item);
  66     if (ok)
  67       ok = items->push_back(static_cast<typename V::value_type>(item));
  68   }
  69
  70   return ok;
  71 }
  72
  73 // Serializes a vector, using delta coding followed by Varint32 coding.
  74 template<typename V>
  75 CheckBool WriteU32Delta(const V& set, SinkStream* buffer) {
  76   size_t count = set.size();
  77   bool ok = buffer->WriteSizeVarint32(count);
  78   uint32 prev = 0;
  79   for (size_t i = 0;  ok && i < count;  ++i) {
  80     uint32 current = set[i];
  81     uint32 delta = current - prev;
  82     ok = buffer->WriteVarint32(delta);
  83     prev = current;
  84   }
  85   return ok;
  86 }
  87
  88 template <typename V>
  89 static CheckBool ReadU32Delta(V* set, SourceStream* buffer) {
  90   uint32 count;
  91
  92   if (!buffer->ReadVarint32(&count))
  93     return false;
  94
  95   set->clear();
  96   bool ok = set->reserve(count);
  97   uint32 prev = 0;
  98
  99   for (size_t i = 0; ok && i < count;  ++i) {
 100     uint32 delta;
 101     ok = buffer->ReadVarint32(&delta);
 102     if (ok) {
 103       uint32 current = prev + delta;
 104       ok = set->push_back(current);
 105       prev = current;
 106     }
 107   }
 108
 109   return ok;
 110 }
 111
 112 // Write a vector as the byte representation of the contents.
 113 //
 114 // (This only really makes sense for a type T that has sizeof(T)==1, otherwise
 115 // serialized representation is not endian-agnostic.  But it is useful to keep
 116 // the possibility of a greater size for experiments comparing Varint32 encoding
 117 // of a vector of larger integrals vs a plain form.)
 118 //
 119 template<typename V>
 120 CheckBool WriteVectorU8(const V& items, SinkStream* buffer) {
 121   size_t count = items.size();
 122   bool ok = buffer->WriteSizeVarint32(count);
 123   if (count != 0 && ok) {
 124     size_t byte_count = count * sizeof(typename V::value_type);
 125     ok = buffer->Write(static_cast<const void*>(&items[0]), byte_count);
 126   }
 127   return ok;
 128 }
 129
 130 template<typename V>
 131 bool ReadVectorU8(V* items, SourceStream* buffer) {
 132   uint32 count;
 133   if (!buffer->ReadVarint32(&count))
 134     return false;
 135
 136   items->clear();
 137   bool ok = items->resize(count, 0);
 138   if (ok && count != 0) {
 139     size_t byte_count = count * sizeof(typename V::value_type);
 140     return buffer->Read(static_cast<void*>(&((*items)[0])), byte_count);
 141   }
 142   return ok;
 143 }
 144
 145 ////////////////////////////////////////////////////////////////////////////////
 146
 147 CheckBool EncodedProgram::DefineRel32Label(int index, RVA value) {
 148   return DefineLabelCommon(&rel32_rva_, index, value);
 149 }
 150
 151 CheckBool EncodedProgram::DefineAbs32Label(int index, RVA value) {
 152   return DefineLabelCommon(&abs32_rva_, index, value);
 153 }
 154
 155 static const RVA kUnassignedRVA = static_cast<RVA>(-1);
 156
 157 CheckBool EncodedProgram::DefineLabelCommon(RvaVector* rvas,
 158                                             int index,
 159                                             RVA rva) {
 160   bool ok = true;
 161   if (static_cast<int>(rvas->size()) <= index)
 162     ok = rvas->resize(index + 1, kUnassignedRVA);
 163
 164   if (ok) {
 165     DCHECK_EQ((*rvas)[index], kUnassignedRVA)
 166         << "DefineLabel double assigned " << index;
 167     (*rvas)[index] = rva;
 168   }
 169
 170   return ok;
 171 }
 172
 173 void EncodedProgram::EndLabels() {
 174   FinishLabelsCommon(&abs32_rva_);
 175   FinishLabelsCommon(&rel32_rva_);
 176 }
 177
 178 void EncodedProgram::FinishLabelsCommon(RvaVector* rvas) {
 179   // Replace all unassigned slots with the value at the previous index so they
 180   // delta-encode to zero.  (There might be better values than zero.  The way to
 181   // get that is have the higher level assembly program assign the unassigned
 182   // slots.)
 183   RVA previous = 0;
 184   size_t size = rvas->size();
 185   for (size_t i = 0;  i < size;  ++i) {
 186     if ((*rvas)[i] == kUnassignedRVA)
 187       (*rvas)[i] = previous;
 188     else
 189       previous = (*rvas)[i];
 190   }
 191 }
 192
 193 CheckBool EncodedProgram::AddOrigin(RVA origin) {
 194   return ops_.push_back(ORIGIN) && origins_.push_back(origin);
 195 }
 196
 197 CheckBool EncodedProgram::AddCopy(size_t count, const void* bytes) {
 198   const uint8* source = static_cast<const uint8*>(bytes);
 199
 200   bool ok = true;
 201
 202   // Fold adjacent COPY instructions into one.  This nearly halves the size of
 203   // an EncodedProgram with only COPY1 instructions since there are approx plain
 204   // 16 bytes per reloc.  This has a working-set benefit during decompression.
 205   // For compression of files with large differences this makes a small (4%)
 206   // improvement in size.  For files with small differences this degrades the
 207   // compressed size by 1.3%
 208   if (!ops_.empty()) {
 209     if (ops_.back() == COPY1) {
 210       ops_.back() = COPY;
 211       ok = copy_counts_.push_back(1);
 212     }
 213     if (ok && ops_.back() == COPY) {
 214       copy_counts_.back() += count;
 215       for (size_t i = 0; ok && i < count; ++i) {
 216         ok = copy_bytes_.push_back(source[i]);
 217       }
 218       return ok;
 219     }
 220   }
 221
 222   if (ok) {
 223     if (count == 1) {
 224       ok = ops_.push_back(COPY1) && copy_bytes_.push_back(source[0]);
 225     } else {
 226       ok = ops_.push_back(COPY) && copy_counts_.push_back(count);
 227       for (size_t i = 0; ok && i < count; ++i) {
 228         ok = copy_bytes_.push_back(source[i]);
 229       }
 230     }
 231   }
 232
 233   return ok;
 234 }
 235
 236 CheckBool EncodedProgram::AddAbs32(int label_index) {
 237   return ops_.push_back(ABS32) && abs32_ix_.push_back(label_index);
 238 }
 239
 240 CheckBool EncodedProgram::AddRel32(int label_index) {
 241   return ops_.push_back(REL32) && rel32_ix_.push_back(label_index);
 242 }
 243
 244 CheckBool EncodedProgram::AddRel32ARM(uint16 op, int label_index) {
 245   return ops_.push_back(static_cast<OP>(op)) &&
 246       rel32_ix_.push_back(label_index);
 247 }
 248
 249 CheckBool EncodedProgram::AddPeMakeRelocs(ExecutableType kind) {
 250   if (kind == EXE_WIN_32_X86)
 251     return ops_.push_back(MAKE_PE_RELOCATION_TABLE);
 252   return ops_.push_back(MAKE_PE64_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   // TODO(sra): Use better configuration.
 296   scoped_ptr<base::Environment> env(base::Environment::Create());
 297   std::string s;
 298   env->GetVar("A_FIELDS", &s);
 299   uint64 fields;
 300   if (!base::StringToUint64(s, &fields))
 301     return static_cast<FieldSelect>(~0);
 302   return static_cast<FieldSelect>(fields);
 303 }
 304
 305 CheckBool EncodedProgram::WriteTo(SinkStreamSet* streams) {
 306   FieldSelect select = GetFieldSelect();
 307
 308   // The order of fields must be consistent in WriteTo and ReadFrom, regardless
 309   // of the streams used.  The code can be configured with all kStreamXXX
 310   // constants the same.
 311   //
 312   // If we change the code to pipeline reading with assembly (to avoid temporary
 313   // storage vectors by consuming operands directly from the stream) then we
 314   // need to read the base address and the random access address tables first,
 315   // the rest can be interleaved.
 316
 317   if (select & INCLUDE_MISC) {
 318     // TODO(sra): write 64 bits.
 319     if (!streams->stream(kStreamMisc)->WriteVarint32(
 320             static_cast<uint32>(image_base_))) {
 321       return false;
 322     }
 323   }
 324
 325   bool success = true;
 326
 327   if (select & INCLUDE_ABS32_ADDRESSES) {
 328     success &= WriteU32Delta(abs32_rva_,
 329                              streams->stream(kStreamAbs32Addresses));
 330   }
 331
 332   if (select & INCLUDE_REL32_ADDRESSES) {
 333     success &= WriteU32Delta(rel32_rva_,
 334                              streams->stream(kStreamRel32Addresses));
 335   }
 336
 337   if (select & INCLUDE_MISC)
 338     success &= WriteVector(origins_, streams->stream(kStreamOriginAddresses));
 339
 340   if (select & INCLUDE_OPS) {
 341     // 5 for length.
 342     success &= streams->stream(kStreamOps)->Reserve(ops_.size() + 5);
 343     success &= WriteVector(ops_, streams->stream(kStreamOps));
 344   }
 345
 346   if (select & INCLUDE_COPY_COUNTS)
 347     success &= WriteVector(copy_counts_, streams->stream(kStreamCopyCounts));
 348
 349   if (select & INCLUDE_BYTES)
 350     success &= WriteVectorU8(copy_bytes_, streams->stream(kStreamBytes));
 351
 352   if (select & INCLUDE_ABS32_INDEXES)
 353     success &= WriteVector(abs32_ix_, streams->stream(kStreamAbs32Indexes));
 354
 355   if (select & INCLUDE_REL32_INDEXES)
 356     success &= WriteVector(rel32_ix_, streams->stream(kStreamRel32Indexes));
 357
 358   return success;
 359 }
 360
 361 bool EncodedProgram::ReadFrom(SourceStreamSet* streams) {
 362   // TODO(sra): read 64 bits.
 363   uint32 temp;
 364   if (!streams->stream(kStreamMisc)->ReadVarint32(&temp))
 365     return false;
 366   image_base_ = temp;
 367
 368   if (!ReadU32Delta(&abs32_rva_, streams->stream(kStreamAbs32Addresses)))
 369     return false;
 370   if (!ReadU32Delta(&rel32_rva_, streams->stream(kStreamRel32Addresses)))
 371     return false;
 372   if (!ReadVector(&origins_, streams->stream(kStreamOriginAddresses)))
 373     return false;
 374   if (!ReadVector(&ops_, streams->stream(kStreamOps)))
 375     return false;
 376   if (!ReadVector(&copy_counts_, streams->stream(kStreamCopyCounts)))
 377     return false;
 378   if (!ReadVectorU8(&copy_bytes_, streams->stream(kStreamBytes)))
 379     return false;
 380   if (!ReadVector(&abs32_ix_, streams->stream(kStreamAbs32Indexes)))
 381     return false;
 382   if (!ReadVector(&rel32_ix_, streams->stream(kStreamRel32Indexes)))
 383     return false;
 384
 385   // Check that streams have been completely consumed.
 386   for (int i = 0;  i < kStreamLimit;  ++i) {
 387     if (streams->stream(i)->Remaining() > 0)
 388       return false;
 389   }
 390
 391   return true;
 392 }
 393
 394 // Safe, non-throwing version of std::vector::at().  Returns 'true' for success,
 395 // 'false' for out-of-bounds index error.
 396 template<typename V, typename T>
 397 bool VectorAt(const V& v, size_t index, T* output) {
 398   if (index >= v.size())
 399     return false;
 400   *output = v[index];
 401   return true;
 402 }
 403
 404 CheckBool EncodedProgram::EvaluateRel32ARM(OP op,
 405                                            size_t& ix_rel32_ix,
 406                                            RVA& current_rva,
 407                                            SinkStream* output) {
 408   switch (op & 0x0000F000) {
 409     case REL32ARM8: {
 410       uint32 index;
 411       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 412         return false;
 413       ++ix_rel32_ix;
 414       RVA rva;
 415       if (!VectorAt(rel32_rva_, index, &rva))
 416         return false;
 417       uint32 decompressed_op;
 418       if (!DisassemblerElf32ARM::Decompress(ARM_OFF8,
 419                                             static_cast<uint16>(op),
 420                                             static_cast<uint32>(rva -
 421                                                                 current_rva),
 422                                             &decompressed_op)) {
 423         return false;
 424       }
 425       uint16 op16 = static_cast<uint16>(decompressed_op);
 426       if (!output->Write(&op16, 2))
 427         return false;
 428       current_rva += 2;
 429       break;
 430     }
 431     case REL32ARM11: {
 432       uint32 index;
 433       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 434         return false;
 435       ++ix_rel32_ix;
 436       RVA rva;
 437       if (!VectorAt(rel32_rva_, index, &rva))
 438         return false;
 439       uint32 decompressed_op;
 440       if (!DisassemblerElf32ARM::Decompress(ARM_OFF11, (uint16) op,
 441                                             (uint32) (rva - current_rva),
 442                                             &decompressed_op)) {
 443         return false;
 444       }
 445       uint16 op16 = static_cast<uint16>(decompressed_op);
 446       if (!output->Write(&op16, 2))
 447         return false;
 448       current_rva += 2;
 449       break;
 450     }
 451     case REL32ARM24: {
 452       uint32 index;
 453       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 454         return false;
 455       ++ix_rel32_ix;
 456       RVA rva;
 457       if (!VectorAt(rel32_rva_, index, &rva))
 458         return false;
 459       uint32 decompressed_op;
 460       if (!DisassemblerElf32ARM::Decompress(ARM_OFF24, (uint16) op,
 461                                             (uint32) (rva - current_rva),
 462                                             &decompressed_op)) {
 463         return false;
 464       }
 465       if (!output->Write(&decompressed_op, 4))
 466         return false;
 467       current_rva += 4;
 468       break;
 469     }
 470     case REL32ARM25: {
 471       uint32 index;
 472       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 473         return false;
 474       ++ix_rel32_ix;
 475       RVA rva;
 476       if (!VectorAt(rel32_rva_, index, &rva))
 477         return false;
 478       uint32 decompressed_op;
 479       if (!DisassemblerElf32ARM::Decompress(ARM_OFF25, (uint16) op,
 480                                             (uint32) (rva - current_rva),
 481                                             &decompressed_op)) {
 482         return false;
 483       }
 484       uint32 words = (decompressed_op << 16) | (decompressed_op >> 16);
 485       if (!output->Write(&words, 4))
 486         return false;
 487       current_rva += 4;
 488       break;
 489     }
 490     case REL32ARM21: {
 491       uint32 index;
 492       if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 493         return false;
 494       ++ix_rel32_ix;
 495       RVA rva;
 496       if (!VectorAt(rel32_rva_, index, &rva))
 497         return false;
 498       uint32 decompressed_op;
 499       if (!DisassemblerElf32ARM::Decompress(ARM_OFF21, (uint16) op,
 500                                             (uint32) (rva - current_rva),
 501                                             &decompressed_op)) {
 502         return false;
 503       }
 504       uint32 words = (decompressed_op << 16) | (decompressed_op >> 16);
 505       if (!output->Write(&words, 4))
 506         return false;
 507       current_rva += 4;
 508       break;
 509     }
 510     default:
 511       return false;
 512   }
 513
 514   return true;
 515 }
 516
 517 CheckBool EncodedProgram::AssembleTo(SinkStream* final_buffer) {
 518   // For the most part, the assembly process walks the various tables.
 519   // ix_mumble is the index into the mumble table.
 520   size_t ix_origins = 0;
 521   size_t ix_copy_counts = 0;
 522   size_t ix_copy_bytes = 0;
 523   size_t ix_abs32_ix = 0;
 524   size_t ix_rel32_ix = 0;
 525
 526   RVA current_rva = 0;
 527
 528   bool pending_pe_relocation_table = false;
 529   uint8 pending_pe_relocation_table_type = 0x03;  // IMAGE_REL_BASED_HIGHLOW
 530   Elf32_Word pending_elf_relocation_table_type = 0;
 531   SinkStream bytes_following_relocation_table;
 532
 533   SinkStream* output = final_buffer;
 534
 535   for (size_t ix_ops = 0;  ix_ops < ops_.size();  ++ix_ops) {
 536     OP op = ops_[ix_ops];
 537
 538     switch (op) {
 539       default:
 540         if (!EvaluateRel32ARM(op, ix_rel32_ix, current_rva, output))
 541           return false;
 542         break;
 543
 544       case ORIGIN: {
 545         RVA section_rva;
 546         if (!VectorAt(origins_, ix_origins, &section_rva))
 547           return false;
 548         ++ix_origins;
 549         current_rva = section_rva;
 550         break;
 551       }
 552
 553       case COPY: {
 554         size_t count;
 555         if (!VectorAt(copy_counts_, ix_copy_counts, &count))
 556           return false;
 557         ++ix_copy_counts;
 558         for (size_t i = 0;  i < count;  ++i) {
 559           uint8 b;
 560           if (!VectorAt(copy_bytes_, ix_copy_bytes, &b))
 561             return false;
 562           ++ix_copy_bytes;
 563           if (!output->Write(&b, 1))
 564             return false;
 565         }
 566         current_rva += static_cast<RVA>(count);
 567         break;
 568       }
 569
 570       case COPY1: {
 571         uint8 b;
 572         if (!VectorAt(copy_bytes_, ix_copy_bytes, &b))
 573           return false;
 574         ++ix_copy_bytes;
 575         if (!output->Write(&b, 1))
 576           return false;
 577         current_rva += 1;
 578         break;
 579       }
 580
 581       case REL32: {
 582         uint32 index;
 583         if (!VectorAt(rel32_ix_, ix_rel32_ix, &index))
 584           return false;
 585         ++ix_rel32_ix;
 586         RVA rva;
 587         if (!VectorAt(rel32_rva_, index, &rva))
 588           return false;
 589         uint32 offset = (rva - (current_rva + 4));
 590         if (!output->Write(&offset, 4))
 591           return false;
 592         current_rva += 4;
 593         break;
 594       }
 595
 596       case ABS32: {
 597         uint32 index;
 598         if (!VectorAt(abs32_ix_, ix_abs32_ix, &index))
 599           return false;
 600         ++ix_abs32_ix;
 601         RVA rva;
 602         if (!VectorAt(abs32_rva_, index, &rva))
 603           return false;
 604         uint32 abs32 = static_cast<uint32>(rva + image_base_);
 605         if (!abs32_relocs_.push_back(current_rva) || !output->Write(&abs32, 4))
 606           return false;
 607         current_rva += 4;
 608         break;
 609       }
 610
 611       case MAKE_PE_RELOCATION_TABLE: {
 612         // We can see the base relocation anywhere, but we only have the
 613         // information to generate it at the very end.  So we divert the bytes
 614         // we are generating to a temporary stream.
 615         if (pending_pe_relocation_table)
 616           return false;  // Can't have two base relocation tables.
 617
 618         pending_pe_relocation_table = true;
 619         output = &bytes_following_relocation_table;
 620         break;
 621         // There is a potential problem *if* the instruction stream contains
 622         // some REL32 relocations following the base relocation and in the same
 623         // section.  We don't know the size of the table, so 'current_rva' will
 624         // be wrong, causing REL32 offsets to be miscalculated.  This never
 625         // happens; the base relocation table is usually in a section of its
 626         // own, a data-only section, and following everything else in the
 627         // executable except some padding zero bytes.  We could fix this by
 628         // emitting an ORIGIN after the MAKE_BASE_RELOCATION_TABLE.
 629       }
 630
 631       case MAKE_PE64_RELOCATION_TABLE: {
 632         if (pending_pe_relocation_table)
 633           return false;  // Can't have two base relocation tables.
 634
 635         pending_pe_relocation_table = true;
 636         pending_pe_relocation_table_type = 0x0A;  // IMAGE_REL_BASED_DIR64
 637         output = &bytes_following_relocation_table;
 638         break;
 639       }
 640
 641       case MAKE_ELF_ARM_RELOCATION_TABLE: {
 642         // We can see the base relocation anywhere, but we only have the
 643         // information to generate it at the very end.  So we divert the bytes
 644         // we are generating to a temporary stream.
 645         if (pending_elf_relocation_table_type)
 646           return false;  // Can't have two base relocation tables.
 647
 648         pending_elf_relocation_table_type = R_ARM_RELATIVE;
 649         output = &bytes_following_relocation_table;
 650         break;
 651       }
 652
 653       case MAKE_ELF_RELOCATION_TABLE: {
 654         // We can see the base relocation anywhere, but we only have the
 655         // information to generate it at the very end.  So we divert the bytes
 656         // we are generating to a temporary stream.
 657         if (pending_elf_relocation_table_type)
 658           return false;  // Can't have two base relocation tables.
 659
 660         pending_elf_relocation_table_type = R_386_RELATIVE;
 661         output = &bytes_following_relocation_table;
 662         break;
 663       }
 664     }
 665   }
 666
 667   if (pending_pe_relocation_table) {
 668     if (!GeneratePeRelocations(final_buffer,
 669                                pending_pe_relocation_table_type) ||
 670         !final_buffer->Append(&bytes_following_relocation_table))
 671       return false;
 672   }
 673
 674   if (pending_elf_relocation_table_type) {
 675     if (!GenerateElfRelocations(pending_elf_relocation_table_type,
 676                                 final_buffer) ||
 677         !final_buffer->Append(&bytes_following_relocation_table))
 678       return false;
 679   }
 680
 681   // Final verification check: did we consume all lists?
 682   if (ix_copy_counts != copy_counts_.size())
 683     return false;
 684   if (ix_copy_bytes != copy_bytes_.size())
 685     return false;
 686   if (ix_abs32_ix != abs32_ix_.size())
 687     return false;
 688   if (ix_rel32_ix != rel32_ix_.size())
 689     return false;
 690
 691   return true;
 692 }
 693
 694 // RelocBlock has the layout of a block of relocations in the base relocation
 695 // table file format.
 696 //
 697 struct RelocBlockPOD {
 698   uint32 page_rva;
 699   uint32 block_size;
 700   uint16 relocs[4096];  // Allow up to one relocation per byte of a 4k page.
 701 };
 702
 703 static_assert(offsetof(RelocBlockPOD, relocs) == 8, "reloc block header size");
 704
 705 class RelocBlock {
 706  public:
 707   RelocBlock() {
 708     pod.page_rva = 0xFFFFFFFF;
 709     pod.block_size = 8;
 710   }
 711
 712   void Add(uint16 item) {
 713     pod.relocs[(pod.block_size-8)/2] = item;
 714     pod.block_size += 2;
 715   }
 716
 717   CheckBool Flush(SinkStream* buffer) WARN_UNUSED_RESULT {
 718     bool ok = true;
 719     if (pod.block_size != 8) {
 720       if (pod.block_size % 4 != 0) {  // Pad to make size multiple of 4 bytes.
 721         Add(0);
 722       }
 723       ok = buffer->Write(&pod, pod.block_size);
 724       pod.block_size = 8;
 725     }
 726     return ok;
 727   }
 728   RelocBlockPOD pod;
 729 };
 730
 731 CheckBool EncodedProgram::GeneratePeRelocations(SinkStream* buffer,
 732                                                 uint8 type) {
 733   std::sort(abs32_relocs_.begin(), abs32_relocs_.end());
 734
 735   RelocBlock block;
 736
 737   bool ok = true;
 738   for (size_t i = 0;  ok && i < abs32_relocs_.size();  ++i) {
 739     uint32 rva = abs32_relocs_[i];
 740     uint32 page_rva = rva & ~0xFFF;
 741     if (page_rva != block.pod.page_rva) {
 742       ok &= block.Flush(buffer);
 743       block.pod.page_rva = page_rva;
 744     }
 745     if (ok)
 746       block.Add(((static_cast<uint16>(type)) << 12) | (rva & 0xFFF));
 747   }
 748   ok &= block.Flush(buffer);
 749   return ok;
 750 }
 751
 752 CheckBool EncodedProgram::GenerateElfRelocations(Elf32_Word r_info,
 753                                                  SinkStream* buffer) {
 754   std::sort(abs32_relocs_.begin(), abs32_relocs_.end());
 755
 756   Elf32_Rel relocation_block;
 757
 758   relocation_block.r_info = r_info;
 759
 760   bool ok = true;
 761   for (size_t i = 0;  ok && i < abs32_relocs_.size();  ++i) {
 762     relocation_block.r_offset = abs32_relocs_[i];
 763     ok = buffer->Write(&relocation_block, sizeof(Elf32_Rel));
 764   }
 765
 766   return ok;
 767 }
 768 ////////////////////////////////////////////////////////////////////////////////
 769
 770 Status WriteEncodedProgram(EncodedProgram* encoded, SinkStreamSet* sink) {
 771   if (!encoded->WriteTo(sink))
 772     return C_STREAM_ERROR;
 773   return C_OK;
 774 }
 775
 776 Status ReadEncodedProgram(SourceStreamSet* streams, EncodedProgram** output) {
 777   EncodedProgram* encoded = new EncodedProgram();
 778   if (encoded->ReadFrom(streams)) {
 779     *output = encoded;
 780     return C_OK;
 781   }
 782   delete encoded;
 783   return C_DESERIALIZATION_FAILED;
 784 }
 785
 786 Status Assemble(EncodedProgram* encoded, SinkStream* buffer) {
 787   bool assembled = encoded->AssembleTo(buffer);
 788   if (assembled)
 789     return C_OK;
 790   return C_ASSEMBLY_FAILED;
 791 }
 792
 793 void DeleteEncodedProgram(EncodedProgram* encoded) {
 794   delete encoded;
 795 }
 796
 797 }  // namespace courgette