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
DwarfStringPool(BumpPtrAllocator & A,AsmPrinter & Asm,StringRef Prefix)20 DwarfStringPool::DwarfStringPool(BumpPtrAllocator &A, AsmPrinter &Asm,
21 StringRef Prefix)
22 : Pool(A), Prefix(Prefix),
23 ShouldCreateSymbols(Asm.doesDwarfUseRelocationsAcrossSections()) {}
24
25 StringMapEntry<DwarfStringPool::EntryTy> &
getEntryImpl(AsmPrinter & Asm,StringRef Str)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
getEntry(AsmPrinter & Asm,StringRef Str)39 DwarfStringPool::EntryRef DwarfStringPool::getEntry(AsmPrinter &Asm,
40 StringRef Str) {
41 auto &MapEntry = getEntryImpl(Asm, Str);
42 return EntryRef(MapEntry);
43 }
44
getIndexedEntry(AsmPrinter & Asm,StringRef Str)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);
51 }
52
emitStringOffsetsTableHeader(AsmPrinter & Asm,MCSection * Section,MCSymbol * StartSym)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
emit(AsmPrinter & Asm,MCSection * StrSection,MCSection * OffsetSection,bool UseRelativeOffsets)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