lib/CodeGen/AsmPrinter/DwarfStringPool.cpp

   1 //===- llvm/CodeGen/DwarfStringPool.cpp - Dwarf Debug Framework -----------===//
   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 #include "DwarfStringPool.h"
  10 #include "llvm/ADT/SmallVector.h"
  11 #include "llvm/ADT/StringRef.h"
  12 #include "llvm/ADT/Twine.h"
  13 #include "llvm/CodeGen/AsmPrinter.h"
  14 #include "llvm/MC/MCAsmInfo.h"
  15 #include "llvm/MC/MCStreamer.h"
  16 #include <cassert>
  17 #include <utility>
  18
  19 using namespace llvm;
  20
  21 DwarfStringPool::DwarfStringPool(BumpPtrAllocator &A, AsmPrinter &Asm,
  22                                  StringRef Prefix)
  23     : Pool(A), Prefix(Prefix),
  24       ShouldCreateSymbols(Asm.MAI->doesDwarfUseRelocationsAcrossSections()) {}
  25
  26 StringMapEntry<DwarfStringPool::EntryTy> &
  27 DwarfStringPool::getEntryImpl(AsmPrinter &Asm, StringRef Str) {
  28   auto I = Pool.insert(std::make_pair(Str, EntryTy()));
  29   auto &Entry = I.first->second;
  30   if (I.second) {
  31     Entry.Index = EntryTy::NotIndexed;
  32     Entry.Offset = NumBytes;
  33     Entry.Symbol = ShouldCreateSymbols ? Asm.createTempSymbol(Prefix) : nullptr;
  34
  35     NumBytes += Str.size() + 1;
  36     assert(NumBytes > Entry.Offset && "Unexpected overflow");
  37   }
  38   return *I.first;
  39 }
  40
  41 DwarfStringPool::EntryRef DwarfStringPool::getEntry(AsmPrinter &Asm,
  42                                                     StringRef Str) {
  43   auto &MapEntry = getEntryImpl(Asm, Str);
  44   return EntryRef(MapEntry, false);
  45 }
  46
  47 DwarfStringPool::EntryRef DwarfStringPool::getIndexedEntry(AsmPrinter &Asm,
  48                                                            StringRef Str) {
  49   auto &MapEntry = getEntryImpl(Asm, Str);
  50   if (!MapEntry.getValue().isIndexed())
  51     MapEntry.getValue().Index = NumIndexedStrings++;
  52   return EntryRef(MapEntry, true);
  53 }
  54
  55 void DwarfStringPool::emitStringOffsetsTableHeader(AsmPrinter &Asm,
  56                                                    MCSection *Section,
  57                                                    MCSymbol *StartSym) {
  58   if (getNumIndexedStrings() == 0)
  59     return;
  60   Asm.OutStreamer->SwitchSection(Section);
  61   unsigned EntrySize = 4;
  62   // FIXME: DWARF64
  63   // We are emitting the header for a contribution to the string offsets
  64   // table. The header consists of an entry with the contribution's
  65   // size (not including the size of the length field), the DWARF version and
  66   // 2 bytes of padding.
  67   Asm.emitInt32(getNumIndexedStrings() * EntrySize + 4);
  68   Asm.emitInt16(Asm.getDwarfVersion());
  69   Asm.emitInt16(0);
  70   // Define the symbol that marks the start of the contribution. It is
  71   // referenced by most unit headers via DW_AT_str_offsets_base.
  72   // Split units do not use the attribute.
  73   if (StartSym)
  74     Asm.OutStreamer->EmitLabel(StartSym);
  75 }
  76
  77 void DwarfStringPool::emit(AsmPrinter &Asm, MCSection *StrSection,
  78                            MCSection *OffsetSection, bool UseRelativeOffsets) {
  79   if (Pool.empty())
  80     return;
  81
  82   // Start the dwarf str section.
  83   Asm.OutStreamer->SwitchSection(StrSection);
  84
  85   // Get all of the string pool entries and sort them by their offset.
  86   SmallVector<const StringMapEntry<EntryTy> *, 64> Entries;
  87   Entries.reserve(Pool.size());
  88
  89   for (const auto &E : Pool)
  90     Entries.push_back(&E);
  91
  92   llvm::sort(Entries, [](const StringMapEntry<EntryTy> *A,
  93                          const StringMapEntry<EntryTy> *B) {
  94     return A->getValue().Offset < B->getValue().Offset;
  95   });
  96
  97   for (const auto &Entry : Entries) {
  98     assert(ShouldCreateSymbols == static_cast<bool>(Entry->getValue().Symbol) &&
  99            "Mismatch between setting and entry");
 100
 101     // Emit a label for reference from debug information entries.
 102     if (ShouldCreateSymbols)
 103       Asm.OutStreamer->EmitLabel(Entry->getValue().Symbol);
 104
 105     // Emit the string itself with a terminating null byte.
 106     Asm.OutStreamer->AddComment("string offset=" +
 107                                 Twine(Entry->getValue().Offset));
 108     Asm.OutStreamer->EmitBytes(
 109         StringRef(Entry->getKeyData(), Entry->getKeyLength() + 1));
 110   }
 111
 112   // If we've got an offset section go ahead and emit that now as well.
 113   if (OffsetSection) {
 114     // Now only take the indexed entries and put them in an array by their ID so
 115     // we can emit them in order.
 116     Entries.resize(NumIndexedStrings);
 117     for (const auto &Entry : Pool) {
 118       if (Entry.getValue().isIndexed())
 119         Entries[Entry.getValue().Index] = &Entry;
 120     }
 121
 122     Asm.OutStreamer->SwitchSection(OffsetSection);
 123     unsigned size = 4; // FIXME: DWARF64 is 8.
 124     for (const auto &Entry : Entries)
 125       if (UseRelativeOffsets)
 126         Asm.emitDwarfStringOffset(Entry->getValue());
 127       else
 128         Asm.OutStreamer->EmitIntValue(Entry->getValue().Offset, size);
 129   }
 130 }