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