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