bolt/lib/Core/BinarySection.cpp

   1 //===- bolt/Core/BinarySection.cpp - Section in a binary file -------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the BinarySection class.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "bolt/Core/BinarySection.h"
  14 #include "bolt/Core/BinaryContext.h"
  15 #include "bolt/Utils/Utils.h"
  16 #include "llvm/MC/MCStreamer.h"
  17 #include "llvm/Support/CommandLine.h"
  18
  19 #define DEBUG_TYPE "bolt"
  20
  21 using namespace llvm;
  22 using namespace bolt;
  23
  24 namespace opts {
  25 extern cl::opt<bool> PrintRelocations;
  26 extern cl::opt<bool> HotData;
  27 } // namespace opts
  28
  29 uint64_t BinarySection::Count = 0;
  30
  31 bool BinarySection::isELF() const { return BC.isELF(); }
  32
  33 bool BinarySection::isMachO() const { return BC.isMachO(); }
  34
  35 uint64_t
  36 BinarySection::hash(const BinaryData &BD,
  37                     std::map<const BinaryData *, uint64_t> &Cache) const {
  38   auto Itr = Cache.find(&BD);
  39   if (Itr != Cache.end())
  40     return Itr->second;
  41
  42   hash_code Hash =
  43       hash_combine(hash_value(BD.getSize()), hash_value(BD.getSectionName()));
  44
  45   Cache[&BD] = Hash;
  46
  47   if (!containsRange(BD.getAddress(), BD.getSize()))
  48     return Hash;
  49
  50   uint64_t Offset = BD.getAddress() - getAddress();
  51   const uint64_t EndOffset = BD.getEndAddress() - getAddress();
  52   auto Begin = Relocations.lower_bound(Relocation{Offset, 0, 0, 0, 0});
  53   auto End = Relocations.upper_bound(Relocation{EndOffset, 0, 0, 0, 0});
  54   const StringRef Contents = getContents();
  55
  56   while (Begin != End) {
  57     const Relocation &Rel = *Begin++;
  58     Hash = hash_combine(
  59         Hash, hash_value(Contents.substr(Offset, Begin->Offset - Offset)));
  60     if (BinaryData *RelBD = BC.getBinaryDataByName(Rel.Symbol->getName()))
  61       Hash = hash_combine(Hash, hash(*RelBD, Cache));
  62     Offset = Rel.Offset + Rel.getSize();
  63   }
  64
  65   Hash = hash_combine(Hash,
  66                       hash_value(Contents.substr(Offset, EndOffset - Offset)));
  67
  68   Cache[&BD] = Hash;
  69
  70   return Hash;
  71 }
  72
  73 void BinarySection::emitAsData(MCStreamer &Streamer,
  74                                const Twine &SectionName) const {
  75   StringRef SectionContents = getContents();
  76   MCSectionELF *ELFSection =
  77       BC.Ctx->getELFSection(SectionName, getELFType(), getELFFlags());
  78
  79   Streamer.switchSection(ELFSection);
  80   Streamer.emitValueToAlignment(getAlign());
  81
  82   if (BC.HasRelocations && opts::HotData && isReordered())
  83     Streamer.emitLabel(BC.Ctx->getOrCreateSymbol("__hot_data_start"));
  84
  85   LLVM_DEBUG(dbgs() << "BOLT-DEBUG: emitting "
  86                     << (isAllocatable() ? "" : "non-")
  87                     << "allocatable data section " << SectionName << '\n');
  88
  89   if (!hasRelocations()) {
  90     Streamer.emitBytes(SectionContents);
  91   } else {
  92     uint64_t SectionOffset = 0;
  93     for (auto RI = Relocations.begin(), RE = Relocations.end(); RI != RE;) {
  94       auto RelocationOffset = RI->Offset;
  95       assert(RelocationOffset < SectionContents.size() && "overflow detected");
  96
  97       if (SectionOffset < RelocationOffset) {
  98         Streamer.emitBytes(SectionContents.substr(
  99             SectionOffset, RelocationOffset - SectionOffset));
 100         SectionOffset = RelocationOffset;
 101       }
 102
 103       // Get iterators to all relocations with the same offset. Usually, there
 104       // is only one such relocation but there can be more for composed
 105       // relocations.
 106       auto ROI = RI;
 107       auto ROE = Relocations.upper_bound(RelocationOffset);
 108
 109       // Start from the next offset on the next iteration.
 110       RI = ROE;
 111
 112       // Skip undefined symbols.
 113       auto HasUndefSym = [this](const auto &Relocation) {
 114         return BC.UndefinedSymbols.count(Relocation.Symbol);
 115       };
 116
 117       if (std::any_of(ROI, ROE, HasUndefSym))
 118         continue;
 119
 120 #ifndef NDEBUG
 121       for (const auto &Relocation : make_range(ROI, ROE)) {
 122         LLVM_DEBUG(
 123             dbgs() << "BOLT-DEBUG: emitting relocation for symbol "
 124                    << (Relocation.Symbol ? Relocation.Symbol->getName()
 125                                          : StringRef("<none>"))
 126                    << " at offset 0x" << Twine::utohexstr(Relocation.Offset)
 127                    << " with size "
 128                    << Relocation::getSizeForType(Relocation.Type) << '\n');
 129       }
 130 #endif
 131
 132       size_t RelocationSize = Relocation::emit(ROI, ROE, &Streamer);
 133       SectionOffset += RelocationSize;
 134     }
 135     assert(SectionOffset <= SectionContents.size() && "overflow error");
 136     if (SectionOffset < SectionContents.size())
 137       Streamer.emitBytes(SectionContents.substr(SectionOffset));
 138   }
 139
 140   if (BC.HasRelocations && opts::HotData && isReordered())
 141     Streamer.emitLabel(BC.Ctx->getOrCreateSymbol("__hot_data_end"));
 142 }
 143
 144 void BinarySection::flushPendingRelocations(raw_pwrite_stream &OS,
 145                                             SymbolResolverFuncTy Resolver) {
 146   if (PendingRelocations.empty() && Patches.empty())
 147     return;
 148
 149   const uint64_t SectionAddress = getAddress();
 150
 151   // We apply relocations to original section contents. For allocatable sections
 152   // this means using their input file offsets, since the output file offset
 153   // could change (e.g. for new instance of .text). For non-allocatable
 154   // sections, the output offset should always be a valid one.
 155   const uint64_t SectionFileOffset =
 156       isAllocatable() ? getInputFileOffset() : getOutputFileOffset();
 157   LLVM_DEBUG(
 158       dbgs() << "BOLT-DEBUG: flushing pending relocations for section "
 159              << getName() << '\n'
 160              << "  address: 0x" << Twine::utohexstr(SectionAddress) << '\n'
 161              << "  offset: 0x" << Twine::utohexstr(SectionFileOffset) << '\n');
 162
 163   for (BinaryPatch &Patch : Patches)
 164     OS.pwrite(Patch.Bytes.data(), Patch.Bytes.size(),
 165               SectionFileOffset + Patch.Offset);
 166
 167   for (Relocation &Reloc : PendingRelocations) {
 168     uint64_t Value = Reloc.Addend;
 169     if (Reloc.Symbol)
 170       Value += Resolver(Reloc.Symbol);
 171
 172     Value = Relocation::encodeValue(Reloc.Type, Value,
 173                                     SectionAddress + Reloc.Offset);
 174
 175     OS.pwrite(reinterpret_cast<const char *>(&Value),
 176               Relocation::getSizeForType(Reloc.Type),
 177               SectionFileOffset + Reloc.Offset);
 178
 179     LLVM_DEBUG(
 180         dbgs() << "BOLT-DEBUG: writing value 0x" << Twine::utohexstr(Value)
 181                << " of size " << Relocation::getSizeForType(Reloc.Type)
 182                << " at section offset 0x" << Twine::utohexstr(Reloc.Offset)
 183                << " address 0x"
 184                << Twine::utohexstr(SectionAddress + Reloc.Offset)
 185                << " file offset 0x"
 186                << Twine::utohexstr(SectionFileOffset + Reloc.Offset) << '\n';);
 187   }
 188
 189   clearList(PendingRelocations);
 190 }
 191
 192 BinarySection::~BinarySection() {
 193   if (isReordered()) {
 194     delete[] getData();
 195     return;
 196   }
 197
 198   if (!isAllocatable() && !hasValidSectionID() &&
 199       (!hasSectionRef() ||
 200        OutputContents.data() != getContents(Section).data())) {
 201     delete[] getOutputData();
 202   }
 203 }
 204
 205 void BinarySection::clearRelocations() { clearList(Relocations); }
 206
 207 void BinarySection::print(raw_ostream &OS) const {
 208   OS << getName() << ", "
 209      << "0x" << Twine::utohexstr(getAddress()) << ", " << getSize() << " (0x"
 210      << Twine::utohexstr(getOutputAddress()) << ", " << getOutputSize() << ")"
 211      << ", data = " << getData() << ", output data = " << getOutputData();
 212
 213   if (isAllocatable())
 214     OS << " (allocatable)";
 215
 216   if (isVirtual())
 217     OS << " (virtual)";
 218
 219   if (isTLS())
 220     OS << " (tls)";
 221
 222   if (opts::PrintRelocations)
 223     for (const Relocation &R : relocations())
 224       OS << "\n  " << R;
 225 }
 226
 227 BinarySection::RelocationSetType
 228 BinarySection::reorderRelocations(bool Inplace) const {
 229   assert(PendingRelocations.empty() &&
 230          "reodering pending relocations not supported");
 231   RelocationSetType NewRelocations;
 232   for (const Relocation &Rel : relocations()) {
 233     uint64_t RelAddr = Rel.Offset + getAddress();
 234     BinaryData *BD = BC.getBinaryDataContainingAddress(RelAddr);
 235     BD = BD->getAtomicRoot();
 236     assert(BD);
 237
 238     if ((!BD->isMoved() && !Inplace) || BD->isJumpTable())
 239       continue;
 240
 241     Relocation NewRel(Rel);
 242     uint64_t RelOffset = RelAddr - BD->getAddress();
 243     NewRel.Offset = BD->getOutputOffset() + RelOffset;
 244     assert(NewRel.Offset < getSize());
 245     LLVM_DEBUG(dbgs() << "BOLT-DEBUG: moving " << Rel << " -> " << NewRel
 246                       << "\n");
 247     NewRelocations.emplace(std::move(NewRel));
 248   }
 249   return NewRelocations;
 250 }
 251
 252 void BinarySection::reorderContents(const std::vector<BinaryData *> &Order,
 253                                     bool Inplace) {
 254   IsReordered = true;
 255
 256   Relocations = reorderRelocations(Inplace);
 257
 258   std::string Str;
 259   raw_string_ostream OS(Str);
 260   const char *Src = Contents.data();
 261   LLVM_DEBUG(dbgs() << "BOLT-DEBUG: reorderContents for " << Name << "\n");
 262   for (BinaryData *BD : Order) {
 263     assert((BD->isMoved() || !Inplace) && !BD->isJumpTable());
 264     assert(BD->isAtomic() && BD->isMoveable());
 265     const uint64_t SrcOffset = BD->getAddress() - getAddress();
 266     assert(SrcOffset < Contents.size());
 267     assert(SrcOffset == BD->getOffset());
 268     while (OS.tell() < BD->getOutputOffset())
 269       OS.write((unsigned char)0);
 270     LLVM_DEBUG(dbgs() << "BOLT-DEBUG: " << BD->getName() << " @ " << OS.tell()
 271                       << "\n");
 272     OS.write(&Src[SrcOffset], BD->getOutputSize());
 273   }
 274   if (Relocations.empty()) {
 275     // If there are no existing relocations, tack a phony one at the end
 276     // of the reordered segment to force LLVM to recognize and map this
 277     // section.
 278     MCSymbol *ZeroSym = BC.registerNameAtAddress("Zero", 0, 0, 0);
 279     addRelocation(OS.tell(), ZeroSym, Relocation::getAbs64(), 0xdeadbeef);
 280
 281     uint64_t Zero = 0;
 282     OS.write(reinterpret_cast<const char *>(&Zero), sizeof(Zero));
 283   }
 284   auto *NewData = reinterpret_cast<char *>(copyByteArray(OS.str()));
 285   Contents = OutputContents = StringRef(NewData, OS.str().size());
 286   OutputSize = Contents.size();
 287 }
 288
 289 std::string BinarySection::encodeELFNote(StringRef NameStr, StringRef DescStr,
 290                                          uint32_t Type) {
 291   std::string Str;
 292   raw_string_ostream OS(Str);
 293   const uint32_t NameSz = NameStr.size() + 1;
 294   const uint32_t DescSz = DescStr.size();
 295   OS.write(reinterpret_cast<const char *>(&(NameSz)), 4);
 296   OS.write(reinterpret_cast<const char *>(&(DescSz)), 4);
 297   OS.write(reinterpret_cast<const char *>(&(Type)), 4);
 298   OS << NameStr << '\0';
 299   for (uint64_t I = NameSz; I < alignTo(NameSz, 4); ++I)
 300     OS << '\0';
 301   OS << DescStr;
 302   for (uint64_t I = DescStr.size(); I < alignTo(DescStr.size(), 4); ++I)
 303     OS << '\0';
 304   return OS.str();
 305 }