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      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