1 //===- llvm/CodeGen/DwarfStringPool.cpp - Dwarf Debug Framework -----------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9
10 #include "DwarfStringPool.h"
11 #include "llvm/ADT/SmallVector.h"
12 #include "llvm/ADT/StringRef.h"
13 #include "llvm/ADT/Twine.h"
14 #include "llvm/CodeGen/AsmPrinter.h"
15 #include "llvm/MC/MCAsmInfo.h"
16 #include "llvm/MC/MCStreamer.h"
17 #include <cassert>
18 #include <utility>
19
20 using namespace llvm;
21
DwarfStringPool(BumpPtrAllocator & A,AsmPrinter & Asm,StringRef Prefix)22 DwarfStringPool::DwarfStringPool(BumpPtrAllocator &A, AsmPrinter &Asm,
23 StringRef Prefix)
24 : Pool(A), Prefix(Prefix),
25 ShouldCreateSymbols(Asm.MAI->doesDwarfUseRelocationsAcrossSections()) {}
26
27 StringMapEntry<DwarfStringPool::EntryTy> &
getEntryImpl(AsmPrinter & Asm,StringRef Str)28 DwarfStringPool::getEntryImpl(AsmPrinter &Asm, StringRef Str) {
29 auto I = Pool.insert(std::make_pair(Str, EntryTy()));
30 auto &Entry = I.first->second;
31 if (I.second) {
32 Entry.Index = EntryTy::NotIndexed;
33 Entry.Offset = NumBytes;
34 Entry.Symbol = ShouldCreateSymbols ? Asm.createTempSymbol(Prefix) : nullptr;
35
36 NumBytes += Str.size() + 1;
37 assert(NumBytes > Entry.Offset && "Unexpected overflow");
38 }
39 return *I.first;
40 }
41
getEntry(AsmPrinter & Asm,StringRef Str)42 DwarfStringPool::EntryRef DwarfStringPool::getEntry(AsmPrinter &Asm,
43 StringRef Str) {
44 auto &MapEntry = getEntryImpl(Asm, Str);
45 return EntryRef(MapEntry, false);
46 }
47
getIndexedEntry(AsmPrinter & Asm,StringRef Str)48 DwarfStringPool::EntryRef DwarfStringPool::getIndexedEntry(AsmPrinter &Asm,
49 StringRef Str) {
50 auto &MapEntry = getEntryImpl(Asm, Str);
51 if (!MapEntry.getValue().isIndexed())
52 MapEntry.getValue().Index = NumIndexedStrings++;
53 return EntryRef(MapEntry, true);
54 }
55
emitStringOffsetsTableHeader(AsmPrinter & Asm,MCSection * Section,MCSymbol * StartSym)56 void DwarfStringPool::emitStringOffsetsTableHeader(AsmPrinter &Asm,
57 MCSection *Section,
58 MCSymbol *StartSym) {
59 if (getNumIndexedStrings() == 0)
60 return;
61 Asm.OutStreamer->SwitchSection(Section);
62 unsigned EntrySize = 4;
63 // FIXME: DWARF64
64 // We are emitting the header for a contribution to the string offsets
65 // table. The header consists of an entry with the contribution's
66 // size (not including the size of the length field), the DWARF version and
67 // 2 bytes of padding.
68 Asm.emitInt32(getNumIndexedStrings() * EntrySize + 4);
69 Asm.emitInt16(Asm.getDwarfVersion());
70 Asm.emitInt16(0);
71 // Define the symbol that marks the start of the contribution. It is
72 // referenced by most unit headers via DW_AT_str_offsets_base.
73 // Split units do not use the attribute.
74 if (StartSym)
75 Asm.OutStreamer->EmitLabel(StartSym);
76 }
77
emit(AsmPrinter & Asm,MCSection * StrSection,MCSection * OffsetSection,bool UseRelativeOffsets)78 void DwarfStringPool::emit(AsmPrinter &Asm, MCSection *StrSection,
79 MCSection *OffsetSection, bool UseRelativeOffsets) {
80 if (Pool.empty())
81 return;
82
83 // Start the dwarf str section.
84 Asm.OutStreamer->SwitchSection(StrSection);
85
86 // Get all of the string pool entries and sort them by their offset.
87 SmallVector<const StringMapEntry<EntryTy> *, 64> Entries;
88 Entries.reserve(Pool.size());
89
90 for (const auto &E : Pool)
91 Entries.push_back(&E);
92
93 llvm::sort(Entries, [](const StringMapEntry<EntryTy> *A,
94 const StringMapEntry<EntryTy> *B) {
95 return A->getValue().Offset < B->getValue().Offset;
96 });
97
98 for (const auto &Entry : Entries) {
99 assert(ShouldCreateSymbols == static_cast<bool>(Entry->getValue().Symbol) &&
100 "Mismatch between setting and entry");
101
102 // Emit a label for reference from debug information entries.
103 if (ShouldCreateSymbols)
104 Asm.OutStreamer->EmitLabel(Entry->getValue().Symbol);
105
106 // Emit the string itself with a terminating null byte.
107 Asm.OutStreamer->AddComment("string offset=" +
108 Twine(Entry->getValue().Offset));
109 Asm.OutStreamer->EmitBytes(
110 StringRef(Entry->getKeyData(), Entry->getKeyLength() + 1));
111 }
112
113 // If we've got an offset section go ahead and emit that now as well.
114 if (OffsetSection) {
115 // Now only take the indexed entries and put them in an array by their ID so
116 // we can emit them in order.
117 Entries.resize(NumIndexedStrings);
118 for (const auto &Entry : Pool) {
119 if (Entry.getValue().isIndexed())
120 Entries[Entry.getValue().Index] = &Entry;
121 }
122
123 Asm.OutStreamer->SwitchSection(OffsetSection);
124 unsigned size = 4; // FIXME: DWARF64 is 8.
125 for (const auto &Entry : Entries)
126 if (UseRelativeOffsets)
127 Asm.emitDwarfStringOffset(Entry->getValue());
128 else
129 Asm.OutStreamer->EmitIntValue(Entry->getValue().Offset, size);
130 }
131 }
132