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 }
131