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
18using namespace llvm;
19
20DwarfStringPool::DwarfStringPool(BumpPtrAllocator &A, AsmPrinter &Asm,
21 StringRef Prefix)
22 : Pool(A), Prefix(Prefix),
23 ShouldCreateSymbols(Asm.doesDwarfUseRelocationsAcrossSections()) {}
24
25StringMapEntry<DwarfStringPool::EntryTy> &
26DwarfStringPool::getEntryImpl(AsmPrinter &Asm, StringRef Str) {
27 auto I = Pool.try_emplace(Key: Str);
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(Name: Prefix) : nullptr;
33
34 NumBytes += Str.size() + 1;
35 }
36 return *I.first;
37}
38
39DwarfStringPool::EntryRef DwarfStringPool::getEntry(AsmPrinter &Asm,
40 StringRef Str) {
41 auto &MapEntry = getEntryImpl(Asm, Str);
42 return EntryRef(MapEntry);
43}
44
45DwarfStringPool::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
53void 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(Length: getNumIndexedStrings() * EntrySize + 4,
65 Comment: "Length of String Offsets Set");
66 Asm.emitInt16(Value: Asm.getDwarfVersion());
67 Asm.emitInt16(Value: 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(Symbol: StartSym);
73}
74
75void 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(Section: StrSection);
82
83 // Get all of the string pool entries and sort them by their offset.
84 SmallVector<const StringMapEntry<EntryTy> *, 64> Entries(
85 llvm::make_pointer_range(Range&: Pool));
86
87 llvm::sort(C&: Entries, Comp: [](const StringMapEntry<EntryTy> *A,
88 const StringMapEntry<EntryTy> *B) {
89 return A->getValue().Offset < B->getValue().Offset;
90 });
91
92 for (const auto &Entry : Entries) {
93 assert(ShouldCreateSymbols == static_cast<bool>(Entry->getValue().Symbol) &&
94 "Mismatch between setting and entry");
95
96 // Emit a label for reference from debug information entries.
97 if (ShouldCreateSymbols)
98 Asm.OutStreamer->emitLabel(Symbol: Entry->getValue().Symbol);
99
100 // Emit the string itself with a terminating null byte.
101 Asm.OutStreamer->AddComment(T: "string offset=" +
102 Twine(Entry->getValue().Offset));
103 Asm.OutStreamer->emitBytes(
104 Data: StringRef(Entry->getKeyData(), Entry->getKeyLength() + 1));
105 }
106
107 // If we've got an offset section go ahead and emit that now as well.
108 if (OffsetSection) {
109 // Now only take the indexed entries and put them in an array by their ID so
110 // we can emit them in order.
111 Entries.resize(N: NumIndexedStrings);
112 for (const auto &Entry : Pool) {
113 if (Entry.getValue().isIndexed())
114 Entries[Entry.getValue().Index] = &Entry;
115 }
116
117 Asm.OutStreamer->switchSection(Section: OffsetSection);
118 unsigned size = Asm.getDwarfOffsetByteSize();
119 for (const auto &Entry : Entries)
120 if (UseRelativeOffsets)
121 Asm.emitDwarfStringOffset(S: Entry->getValue());
122 else
123 Asm.OutStreamer->emitIntValue(Value: Entry->getValue().Offset, Size: size);
124 }
125}
126