[BOLT][DWARF][NFC] Refactor GDB Index into a new file (#94405)

Create a new class and file for functions that update GDB index.

Author: sayhaan

bolt/include/bolt/Core/GDBIndex.h

@@ -0,0 +1,61 @@
+//===-- bolt/Core/GDBIndex.h - GDB Index support ----------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// This file contains declaration of classes required for generation of
+/// .gdb_index section.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef BOLT_CORE_GDB_INDEX_H
+#define BOLT_CORE_GDB_INDEX_H
+
+#include "bolt/Core/BinaryContext.h"
+#include <vector>
+
+namespace llvm {
+namespace bolt {
+
+class GDBIndex {
+public:
+  /// Contains information about TU so we can write out correct entries in GDB
+  /// index.
+  struct GDBIndexTUEntry {
+    uint64_t UnitOffset;
+    uint64_t TypeHash;
+    uint64_t TypeDIERelativeOffset;
+  };
+
+private:
+  BinaryContext &BC;
+
+  /// Entries for GDB Index Types CU List.
+  using GDBIndexTUEntryType = std::vector<GDBIndexTUEntry>;
+  GDBIndexTUEntryType GDBIndexTUEntryVector;
+
+public:
+  GDBIndex(BinaryContext &BC) : BC(BC) {}
+
+  std::mutex GDBIndexMutex;
+
+  /// Adds an GDBIndexTUEntry if .gdb_index section exists.
+  void addGDBTypeUnitEntry(const GDBIndexTUEntry &&Entry);
+
+  /// Rewrite .gdb_index section if present.
+  void updateGdbIndexSection(const CUOffsetMap &CUMap, const uint32_t NumCUs,
+                             DebugARangesSectionWriter &ARangesSectionWriter);
+
+  /// Returns all entries needed for Types CU list.
+  const GDBIndexTUEntryType &getGDBIndexTUEntryVector() const {
+    return GDBIndexTUEntryVector;
+  }
+};
+
+} // namespace bolt
+} // namespace llvm
+
+#endif

bolt/lib/Core/CMakeLists.txt

@@ -25,6 +25,7 @@ add_llvm_library(LLVMBOLTCore
   DynoStats.cpp
   Exceptions.cpp
   FunctionLayout.cpp
+  GDBIndex.cpp
   HashUtilities.cpp
   JumpTable.cpp
   MCPlusBuilder.cpp

bolt/lib/Core/GDBIndex.cpp

@@ -0,0 +1,185 @@
+//===- bolt/Core/GDBIndex.cpp  - GDB Index support ------------------------===//
+//
+// 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/Core/GDBIndex.h"
+
+using namespace llvm::bolt;
+using namespace llvm::support::endian;
+
+void GDBIndex::addGDBTypeUnitEntry(const GDBIndexTUEntry &&Entry) {
+  std::lock_guard<std::mutex> Lock(GDBIndexMutex);
+  if (!BC.getGdbIndexSection())
+    return;
+  GDBIndexTUEntryVector.emplace_back(Entry);
+}
+
+void GDBIndex::updateGdbIndexSection(
+    const CUOffsetMap &CUMap, const uint32_t NumCUs,
+    DebugARangesSectionWriter &ARangesSectionWriter) {
+  if (!BC.getGdbIndexSection())
+    return;
+
+  // See https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html
+  // for .gdb_index section format.
+
+  StringRef GdbIndexContents = BC.getGdbIndexSection()->getContents();
+
+  const char *Data = GdbIndexContents.data();
+
+  // Parse the header.
+  const uint32_t Version = read32le(Data);
+  if (Version != 7 && Version != 8) {
+    errs() << "BOLT-ERROR: can only process .gdb_index versions 7 and 8\n";
+    exit(1);
+  }
+
+  // Some .gdb_index generators use file offsets while others use section
+  // offsets. Hence we can only rely on offsets relative to each other,
+  // and ignore their absolute values.
+  const uint32_t CUListOffset = read32le(Data + 4);
+  const uint32_t CUTypesOffset = read32le(Data + 8);
+  const uint32_t AddressTableOffset = read32le(Data + 12);
+  const uint32_t SymbolTableOffset = read32le(Data + 16);
+  const uint32_t ConstantPoolOffset = read32le(Data + 20);
+  Data += 24;
+
+  // Map CUs offsets to indices and verify existing index table.
+  std::map<uint32_t, uint32_t> OffsetToIndexMap;
+  const uint32_t CUListSize = CUTypesOffset - CUListOffset;
+  const uint32_t TUListSize = AddressTableOffset - CUTypesOffset;
+  const unsigned NUmCUsEncoded = CUListSize / 16;
+  unsigned MaxDWARFVersion = BC.DwCtx->getMaxVersion();
+  unsigned NumDWARF5TUs =
+      getGDBIndexTUEntryVector().size() - BC.DwCtx->getNumTypeUnits();
+  bool SkipTypeUnits = false;
+  // For DWARF5 Types are in .debug_info.
+  // LLD doesn't generate Types CU List, and in CU list offset
+  // only includes CUs.
+  // GDB 11+ includes only CUs in CU list and generates Types
+  // list.
+  // GDB 9 includes CUs and TUs in CU list and generates TYpes
+  // list. The NumCUs is CUs + TUs, so need to modify the check.
+  // For split-dwarf
+  // GDB-11, DWARF5: TU units from dwo are not included.
+  // GDB-11, DWARF4: TU units from dwo are included.
+  if (MaxDWARFVersion >= 5)
+    SkipTypeUnits = !TUListSize ? true
+                                : ((NUmCUsEncoded + NumDWARF5TUs) ==
+                                   BC.DwCtx->getNumCompileUnits());
+
+  if (!((CUListSize == NumCUs * 16) ||
+        (CUListSize == (NumCUs + NumDWARF5TUs) * 16))) {
+    errs() << "BOLT-ERROR: .gdb_index: CU count mismatch\n";
+    exit(1);
+  }
+  DenseSet<uint64_t> OriginalOffsets;
+  for (unsigned Index = 0, Units = BC.DwCtx->getNumCompileUnits();
+       Index < Units; ++Index) {
+    const DWARFUnit *CU = BC.DwCtx->getUnitAtIndex(Index);
+    if (SkipTypeUnits && CU->isTypeUnit())
+      continue;
+    const uint64_t Offset = read64le(Data);
+    Data += 16;
+    if (CU->getOffset() != Offset) {
+      errs() << "BOLT-ERROR: .gdb_index CU offset mismatch\n";
+      exit(1);
+    }
+
+    OriginalOffsets.insert(Offset);
+    OffsetToIndexMap[Offset] = Index;
+  }
+
+  // Ignore old address table.
+  const uint32_t OldAddressTableSize = SymbolTableOffset - AddressTableOffset;
+  // Move Data to the beginning of symbol table.
+  Data += SymbolTableOffset - CUTypesOffset;
+
+  // Calculate the size of the new address table.
+  uint32_t NewAddressTableSize = 0;
+  for (const auto &CURangesPair : ARangesSectionWriter.getCUAddressRanges()) {
+    const SmallVector<DebugAddressRange, 2> &Ranges = CURangesPair.second;
+    NewAddressTableSize += Ranges.size() * 20;
+  }
+
+  // Difference between old and new table (and section) sizes.
+  // Could be negative.
+  int32_t Delta = NewAddressTableSize - OldAddressTableSize;
+
+  size_t NewGdbIndexSize = GdbIndexContents.size() + Delta;
+
+  // Free'd by ExecutableFileMemoryManager.
+  auto *NewGdbIndexContents = new uint8_t[NewGdbIndexSize];
+  uint8_t *Buffer = NewGdbIndexContents;
+
+  write32le(Buffer, Version);
+  write32le(Buffer + 4, CUListOffset);
+  write32le(Buffer + 8, CUTypesOffset);
+  write32le(Buffer + 12, AddressTableOffset);
+  write32le(Buffer + 16, SymbolTableOffset + Delta);
+  write32le(Buffer + 20, ConstantPoolOffset + Delta);
+  Buffer += 24;
+
+  using MapEntry = std::pair<uint32_t, CUInfo>;
+  std::vector<MapEntry> CUVector(CUMap.begin(), CUMap.end());
+  // Need to sort since we write out all of TUs in .debug_info before CUs.
+  std::sort(CUVector.begin(), CUVector.end(),
+            [](const MapEntry &E1, const MapEntry &E2) -> bool {
+              return E1.second.Offset < E2.second.Offset;
+            });
+  // Writing out CU List <Offset, Size>
+  for (auto &CUInfo : CUVector) {
+    // Skipping TU for DWARF5 when they are not included in CU list.
+    if (!OriginalOffsets.count(CUInfo.first))
+      continue;
+    write64le(Buffer, CUInfo.second.Offset);
+    // Length encoded in CU doesn't contain first 4 bytes that encode length.
+    write64le(Buffer + 8, CUInfo.second.Length + 4);
+    Buffer += 16;
+  }
+
+  // Rewrite TU CU List, since abbrevs can be different.
+  // Entry example:
+  // 0: offset = 0x00000000, type_offset = 0x0000001e, type_signature =
+  // 0x418503b8111e9a7b Spec says " triplet, the first value is the CU offset,
+  // the second value is the type offset in the CU, and the third value is the
+  // type signature" Looking at what is being generated by gdb-add-index. The
+  // first entry is TU offset, second entry is offset from it, and third entry
+  // is the type signature.
+  if (TUListSize)
+    for (const GDBIndexTUEntry &Entry : getGDBIndexTUEntryVector()) {
+      write64le(Buffer, Entry.UnitOffset);
+      write64le(Buffer + 8, Entry.TypeDIERelativeOffset);
+      write64le(Buffer + 16, Entry.TypeHash);
+      Buffer += sizeof(GDBIndexTUEntry);
+    }
+
+  // Generate new address table.
+  for (const std::pair<const uint64_t, DebugAddressRangesVector> &CURangesPair :
+       ARangesSectionWriter.getCUAddressRanges()) {
+    const uint32_t CUIndex = OffsetToIndexMap[CURangesPair.first];
+    const DebugAddressRangesVector &Ranges = CURangesPair.second;
+    for (const DebugAddressRange &Range : Ranges) {
+      write64le(Buffer, Range.LowPC);
+      write64le(Buffer + 8, Range.HighPC);
+      write32le(Buffer + 16, CUIndex);
+      Buffer += 20;
+    }
+  }
+
+  const size_t TrailingSize =
+      GdbIndexContents.data() + GdbIndexContents.size() - Data;
+  assert(Buffer + TrailingSize == NewGdbIndexContents + NewGdbIndexSize &&
+         "size calculation error");
+
+  // Copy over the rest of the original data.
+  memcpy(Buffer, Data, TrailingSize);
+
+  // Register the new section.
+  BC.registerOrUpdateNoteSection(".gdb_index", NewGdbIndexContents,
+                                 NewGdbIndexSize);
+}