bolt/lib/Profile/BoltAddressTranslation.cpp

//===- bolt/Profile/BoltAddressTranslation.cpp ----------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "bolt/Profile/BoltAddressTranslation.h"
#include "bolt/Core/BinaryFunction.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/LEB128.h"

#define DEBUG_TYPE "bolt-bat"

namespace llvm {
namespace bolt {

const char *BoltAddressTranslation::SECTION_NAME = ".note.bolt_bat";

void BoltAddressTranslation::writeEntriesForBB(MapTy &Map,
                                               const BinaryBasicBlock &BB,
                                               uint64_t FuncAddress) {
  const uint64_t BBOutputOffset =
      BB.getOutputAddressRange().first - FuncAddress;
  const uint32_t BBInputOffset = BB.getInputOffset();

  // Every output BB must track back to an input BB for profile collection
  // in bolted binaries. If we are missing an offset, it means this block was
  // created by a pass. We will skip writing any entries for it, and this means
  // any traffic happening in this block will map to the previous block in the
  // layout. This covers the case where an input basic block is split into two,
  // and the second one lacks any offset.
  if (BBInputOffset == BinaryBasicBlock::INVALID_OFFSET)
    return;

  LLVM_DEBUG(dbgs() << "BB " << BB.getName() << "\n");
  LLVM_DEBUG(dbgs() << "  Key: " << Twine::utohexstr(BBOutputOffset)
                    << " Val: " << Twine::utohexstr(BBInputOffset) << "\n");
  // In case of conflicts (same Key mapping to different Vals), the last
  // update takes precedence. Of course it is not ideal to have conflicts and
  // those happen when we have an empty BB that either contained only
  // NOPs or a jump to the next block (successor). Either way, the successor
  // and this deleted block will both share the same output address (the same
  // key), and we need to map back. We choose here to privilege the successor by
  // allowing it to overwrite the previously inserted key in the map.
  Map[BBOutputOffset] = BBInputOffset << 1;

  const auto &IOAddressMap =
      BB.getFunction()->getBinaryContext().getIOAddressMap();

  for (const auto &[InputOffset, Sym] : BB.getLocSyms()) {
    const auto InputAddress = BB.getFunction()->getAddress() + InputOffset;
    const auto OutputAddress = IOAddressMap.lookup(InputAddress);
    assert(OutputAddress && "Unknown instruction address");
    const auto OutputOffset = *OutputAddress - FuncAddress;

    // Is this the first instruction in the BB? No need to duplicate the entry.
    if (OutputOffset == BBOutputOffset)
      continue;

    LLVM_DEBUG(dbgs() << "  Key: " << Twine::utohexstr(OutputOffset) << " Val: "
                      << Twine::utohexstr(InputOffset) << " (branch)\n");
    Map.insert(std::pair<uint32_t, uint32_t>(OutputOffset,
                                             (InputOffset << 1) | BRANCHENTRY));
  }
}

void BoltAddressTranslation::write(const BinaryContext &BC, raw_ostream &OS) {
  LLVM_DEBUG(dbgs() << "BOLT-DEBUG: Writing BOLT Address Translation Tables\n");
  for (auto &BFI : BC.getBinaryFunctions()) {
    const BinaryFunction &Function = BFI.second;
    // We don't need a translation table if the body of the function hasn't
    // changed
    if (Function.isIgnored() || (!BC.HasRelocations && !Function.isSimple()))
      continue;

    LLVM_DEBUG(dbgs() << "Function name: " << Function.getPrintName() << "\n");
    LLVM_DEBUG(dbgs() << " Address reference: 0x"
                      << Twine::utohexstr(Function.getOutputAddress()) << "\n");

    MapTy Map;
    for (const BinaryBasicBlock *const BB :
         Function.getLayout().getMainFragment())
      writeEntriesForBB(Map, *BB, Function.getOutputAddress());
    Maps.emplace(Function.getOutputAddress(), std::move(Map));

    if (!Function.isSplit())
      continue;

    // Split maps
    LLVM_DEBUG(dbgs() << " Cold part\n");
    for (const FunctionFragment &FF :
         Function.getLayout().getSplitFragments()) {
      Map.clear();
      for (const BinaryBasicBlock *const BB : FF)
        writeEntriesForBB(Map, *BB, FF.getAddress());

      Maps.emplace(FF.getAddress(), std::move(Map));
      ColdPartSource.emplace(FF.getAddress(), Function.getOutputAddress());
    }
  }

  // Output addresses are delta-encoded
  uint64_t PrevAddress = 0;
  writeMaps</*Cold=*/false>(Maps, PrevAddress, OS);
  writeMaps</*Cold=*/true>(Maps, PrevAddress, OS);

  outs() << "BOLT-INFO: Wrote " << Maps.size() << " BAT maps\n";
}

template <bool Cold>
void BoltAddressTranslation::writeMaps(std::map<uint64_t, MapTy> &Maps,
                                       uint64_t &PrevAddress, raw_ostream &OS) {
  const uint32_t NumFuncs =
      llvm::count_if(llvm::make_first_range(Maps), [&](const uint64_t Address) {
        return Cold == ColdPartSource.count(Address);
      });
  encodeULEB128(NumFuncs, OS);
  LLVM_DEBUG(dbgs() << "Writing " << NumFuncs << (Cold ? " cold" : "")
                    << " functions for BAT.\n");
  size_t PrevIndex = 0;
  for (auto &MapEntry : Maps) {
    const uint64_t Address = MapEntry.first;
    // Only process cold fragments in cold mode, and vice versa.
    if (Cold != ColdPartSource.count(Address))
      continue;
    MapTy &Map = MapEntry.second;
    const uint32_t NumEntries = Map.size();
    LLVM_DEBUG(dbgs() << "Writing " << NumEntries << " entries for 0x"
                      << Twine::utohexstr(Address) << ".\n");
    encodeULEB128(Address - PrevAddress, OS);
    PrevAddress = Address;
    if (Cold) {
      size_t HotIndex =
          std::distance(ColdPartSource.begin(), ColdPartSource.find(Address));
      encodeULEB128(HotIndex - PrevIndex, OS);
      PrevIndex = HotIndex;
    }
    encodeULEB128(NumEntries, OS);
    uint64_t InOffset = 0;
    // Output and Input addresses and delta-encoded
    for (std::pair<const uint32_t, uint32_t> &KeyVal : Map) {
      const uint64_t OutputAddress = KeyVal.first + Address;
      encodeULEB128(OutputAddress - PrevAddress, OS);
      PrevAddress = OutputAddress;
      encodeSLEB128(KeyVal.second - InOffset, OS);
      InOffset = KeyVal.second;
    }
  }
}

std::error_code BoltAddressTranslation::parse(StringRef Buf) {
  DataExtractor DE = DataExtractor(Buf, true, 8);
  uint64_t Offset = 0;
  if (Buf.size() < 12)
    return make_error_code(llvm::errc::io_error);

  const uint32_t NameSz = DE.getU32(&Offset);
  const uint32_t DescSz = DE.getU32(&Offset);
  const uint32_t Type = DE.getU32(&Offset);

  if (Type != BinarySection::NT_BOLT_BAT ||
      Buf.size() + Offset < alignTo(NameSz, 4) + DescSz)
    return make_error_code(llvm::errc::io_error);

  StringRef Name = Buf.slice(Offset, Offset + NameSz);
  Offset = alignTo(Offset + NameSz, 4);
  if (Name.substr(0, 4) != "BOLT")
    return make_error_code(llvm::errc::io_error);

  Error Err(Error::success());
  std::vector<uint64_t> HotFuncs;
  uint64_t PrevAddress = 0;
  parseMaps</*Cold=*/false>(HotFuncs, PrevAddress, DE, Offset, Err);
  parseMaps</*Cold=*/true>(HotFuncs, PrevAddress, DE, Offset, Err);
  outs() << "BOLT-INFO: Parsed " << Maps.size() << " BAT entries\n";
  return errorToErrorCode(std::move(Err));
}

template <bool Cold>
void BoltAddressTranslation::parseMaps(std::vector<uint64_t> &HotFuncs,
                                       uint64_t &PrevAddress, DataExtractor &DE,
                                       uint64_t &Offset, Error &Err) {
  const uint32_t NumFunctions = DE.getULEB128(&Offset, &Err);
  LLVM_DEBUG(dbgs() << "Parsing " << NumFunctions << (Cold ? " cold" : "")
                    << " functions\n");
  size_t HotIndex = 0;
  for (uint32_t I = 0; I < NumFunctions; ++I) {
    const uint64_t Address = PrevAddress + DE.getULEB128(&Offset, &Err);
    PrevAddress = Address;
    if (Cold) {
      HotIndex += DE.getULEB128(&Offset, &Err);
      ColdPartSource.emplace(Address, HotFuncs[HotIndex]);
    } else {
      HotFuncs.push_back(Address);
    }
    const uint32_t NumEntries = DE.getULEB128(&Offset, &Err);
    MapTy Map;

    LLVM_DEBUG(dbgs() << "Parsing " << NumEntries << " entries for 0x"
                      << Twine::utohexstr(Address) << "\n");
    uint64_t InputOffset = 0;
    for (uint32_t J = 0; J < NumEntries; ++J) {
      const uint64_t OutputDelta = DE.getULEB128(&Offset, &Err);
      const uint64_t OutputAddress = PrevAddress + OutputDelta;
      const uint64_t OutputOffset = OutputAddress - Address;
      PrevAddress = OutputAddress;
      const int64_t InputDelta = DE.getSLEB128(&Offset, &Err);
      InputOffset += InputDelta;
      Map.insert(std::pair<uint32_t, uint32_t>(OutputOffset, InputOffset));
      LLVM_DEBUG(
          dbgs() << formatv("{0:x} -> {1:x} ({2}/{3}b -> {4}/{5}b), {6:x}\n",
                            OutputOffset, InputOffset, OutputDelta,
                            encodeULEB128(OutputDelta, nulls()), InputDelta,
                            encodeSLEB128(InputDelta, nulls()), OutputAddress));
    }
    Maps.insert(std::pair<uint64_t, MapTy>(Address, Map));
  }
}

void BoltAddressTranslation::dump(raw_ostream &OS) {
  const size_t NumTables = Maps.size();
  OS << "BAT tables for " << NumTables << " functions:\n";
  for (const auto &MapEntry : Maps) {
    OS << "Function Address: 0x" << Twine::utohexstr(MapEntry.first) << "\n";
    OS << "BB mappings:\n";
    for (const auto &Entry : MapEntry.second) {
      const bool IsBranch = Entry.second & BRANCHENTRY;
      const uint32_t Val = Entry.second >> 1; // dropping BRANCHENTRY bit
      OS << "0x" << Twine::utohexstr(Entry.first) << " -> "
         << "0x" << Twine::utohexstr(Val);
      if (IsBranch)
        OS << " (branch)";
      OS << "\n";
    }
    OS << "\n";
  }
  const size_t NumColdParts = ColdPartSource.size();
  if (!NumColdParts)
    return;

  OS << NumColdParts << " cold mappings:\n";
  for (const auto &Entry : ColdPartSource) {
    OS << "0x" << Twine::utohexstr(Entry.first) << " -> "
       << Twine::utohexstr(Entry.second) << "\n";
  }
  OS << "\n";
}

uint64_t BoltAddressTranslation::translate(uint64_t FuncAddress,
                                           uint64_t Offset,
                                           bool IsBranchSrc) const {
  auto Iter = Maps.find(FuncAddress);
  if (Iter == Maps.end())
    return Offset;

  const MapTy &Map = Iter->second;
  auto KeyVal = Map.upper_bound(Offset);
  if (KeyVal == Map.begin())
    return Offset;

  --KeyVal;

  const uint32_t Val = KeyVal->second >> 1; // dropping BRANCHENTRY bit
  // Branch source addresses are translated to the first instruction of the
  // source BB to avoid accounting for modifications BOLT may have made in the
  // BB regarding deletion/addition of instructions.
  if (IsBranchSrc)
    return Val;
  return Offset - KeyVal->first + Val;
}

std::optional<BoltAddressTranslation::FallthroughListTy>
BoltAddressTranslation::getFallthroughsInTrace(uint64_t FuncAddress,
                                               uint64_t From,
                                               uint64_t To) const {
  SmallVector<std::pair<uint64_t, uint64_t>, 16> Res;

  // Filter out trivial case
  if (From >= To)
    return Res;

  From -= FuncAddress;
  To -= FuncAddress;

  auto Iter = Maps.find(FuncAddress);
  if (Iter == Maps.end())
    return std::nullopt;

  const MapTy &Map = Iter->second;
  auto FromIter = Map.upper_bound(From);
  if (FromIter == Map.begin())
    return Res;
  // Skip instruction entries, to create fallthroughs we are only interested in
  // BB boundaries
  do {
    if (FromIter == Map.begin())
      return Res;
    --FromIter;
  } while (FromIter->second & BRANCHENTRY);

  auto ToIter = Map.upper_bound(To);
  if (ToIter == Map.begin())
    return Res;
  --ToIter;
  if (FromIter->first >= ToIter->first)
    return Res;

  for (auto Iter = FromIter; Iter != ToIter;) {
    const uint32_t Src = Iter->first;
    if (Iter->second & BRANCHENTRY) {
      ++Iter;
      continue;
    }

    ++Iter;
    while (Iter->second & BRANCHENTRY && Iter != ToIter)
      ++Iter;
    if (Iter->second & BRANCHENTRY)
      break;
    Res.emplace_back(Src, Iter->first);
  }

  return Res;
}

uint64_t BoltAddressTranslation::fetchParentAddress(uint64_t Address) const {
  auto Iter = ColdPartSource.find(Address);
  if (Iter == ColdPartSource.end())
    return 0;
  return Iter->second;
}

bool BoltAddressTranslation::enabledFor(
    llvm::object::ELFObjectFileBase *InputFile) const {
  for (const SectionRef &Section : InputFile->sections()) {
    Expected<StringRef> SectionNameOrErr = Section.getName();
    if (Error E = SectionNameOrErr.takeError())
      continue;

    if (SectionNameOrErr.get() == SECTION_NAME)
      return true;
  }
  return false;
}
} // namespace bolt
} // namespace llvm