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
19using namespace llvm;
20
21DwarfStringPool::DwarfStringPool(BumpPtrAllocator &A, AsmPrinter &Asm,
22                                 StringRef Prefix)
23    : Pool(A), Prefix(Prefix),
24      ShouldCreateSymbols(Asm.MAI->doesDwarfUseRelocationsAcrossSections()) {}
25
26StringMapEntry<DwarfStringPool::EntryTy> &
27DwarfStringPool::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
41DwarfStringPool::EntryRef DwarfStringPool::getEntry(AsmPrinter &Asm,
42                                                    StringRef Str) {
43  auto &MapEntry = getEntryImpl(Asm, Str);
44  return EntryRef(MapEntry, false);
45}
46
47DwarfStringPool::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
55void 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
77void 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}
131