206 lines
7.7 KiB
C++
206 lines
7.7 KiB
C++
//===- GdbIndex.cpp -------------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// File contains classes for implementation of --gdb-index command line option.
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//
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// If that option is used, linker should emit a .gdb_index section that allows
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// debugger to locate and read .dwo files, containing neccessary debug
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// information.
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// More information about implementation can be found in DWARF specification,
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// latest version is available at http://dwarfstd.org.
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//
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// .gdb_index section format:
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// (Information is based on/taken from
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// https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html (*))
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//
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// A mapped index consists of several areas, laid out in order:
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// 1) The file header.
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// 2) "The CU (compilation unit) list. This is a sequence of pairs of 64-bit
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// little-endian values, sorted by the CU offset. The first element in each
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// pair is the offset of a CU in the .debug_info section. The second element
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// in each pair is the length of that CU. References to a CU elsewhere in the
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// map are done using a CU index, which is just the 0-based index into this
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// table. Note that if there are type CUs, then conceptually CUs and type CUs
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// form a single list for the purposes of CU indices."(*)
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// 3) The types CU list. Depricated as .debug_types does not appear in the DWARF
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// v5 specification.
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// 4) The address area. The address area is a sequence of address
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// entries, where each entrie contains low address, high address and CU
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// index.
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// 5) "The symbol table. This is an open-addressed hash table. The size of the
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// hash table is always a power of 2. Each slot in the hash table consists of
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// a pair of offset_type values. The first value is the offset of the
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// symbol's name in the constant pool. The second value is the offset of the
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// CU vector in the constant pool."(*)
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// 6) "The constant pool. This is simply a bunch of bytes. It is organized so
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// that alignment is correct: CU vectors are stored first, followed by
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// strings." (*)
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//
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// For constructing the .gdb_index section following steps should be performed:
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// 1) For file header nothing special should be done. It contains the offsets to
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// the areas below.
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// 2) Scan the compilation unit headers of the .debug_info sections to build a
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// list of compilation units.
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// 3) CU Types are no longer needed as DWARF skeleton type units never made it
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// into the standard. lld does nothing to support parsing of .debug_types
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// and generates empty types CU area in .gdb_index section.
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// 4) Address area entries are extracted from DW_TAG_compile_unit DIEs of
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// .debug_info sections.
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// 5) For building the symbol table linker extracts the public names from the
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// .debug_gnu_pubnames and .debug_gnu_pubtypes sections. Then it builds the
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// hashtable in according to .gdb_index format specification.
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// 6) Constant pool is populated at the same time as symbol table.
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//===----------------------------------------------------------------------===//
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#include "GdbIndex.h"
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#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
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#include "llvm/Object/ELFObjectFile.h"
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using namespace llvm;
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using namespace llvm::object;
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using namespace lld::elf;
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template <class ELFT>
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GdbIndexBuilder<ELFT>::GdbIndexBuilder(InputSection<ELFT> *DebugInfoSec)
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: DebugInfoSec(DebugInfoSec) {
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if (Expected<std::unique_ptr<object::ObjectFile>> Obj =
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object::ObjectFile::createObjectFile(DebugInfoSec->getFile()->MB))
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Dwarf.reset(new DWARFContextInMemory(*Obj.get(), this));
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else
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error(toString(DebugInfoSec->getFile()) + ": error creating DWARF context");
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}
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template <class ELFT>
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std::vector<std::pair<typename ELFT::uint, typename ELFT::uint>>
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GdbIndexBuilder<ELFT>::readCUList() {
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std::vector<std::pair<uintX_t, uintX_t>> Ret;
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for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf->compile_units())
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Ret.push_back(
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{DebugInfoSec->OutSecOff + CU->getOffset(), CU->getLength() + 4});
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return Ret;
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}
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template <class ELFT>
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std::vector<std::pair<StringRef, uint8_t>>
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GdbIndexBuilder<ELFT>::readPubNamesAndTypes() {
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const bool IsLE = ELFT::TargetEndianness == llvm::support::little;
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StringRef Data[] = {Dwarf->getGnuPubNamesSection(),
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Dwarf->getGnuPubTypesSection()};
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std::vector<std::pair<StringRef, uint8_t>> Ret;
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for (StringRef D : Data) {
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DWARFDebugPubTable PubTable(D, IsLE, true);
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for (const DWARFDebugPubTable::Set &S : PubTable.getData())
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for (const DWARFDebugPubTable::Entry &E : S.Entries)
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Ret.push_back({E.Name, E.Descriptor.toBits()});
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}
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return Ret;
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}
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std::pair<bool, GdbSymbol *> GdbHashTab::add(uint32_t Hash, size_t Offset) {
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if (Size * 4 / 3 >= Table.size())
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expand();
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GdbSymbol **Slot = findSlot(Hash, Offset);
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bool New = false;
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if (*Slot == nullptr) {
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++Size;
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*Slot = new (Alloc) GdbSymbol(Hash, Offset);
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New = true;
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}
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return {New, *Slot};
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}
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void GdbHashTab::expand() {
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if (Table.empty()) {
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Table.resize(InitialSize);
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return;
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}
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std::vector<GdbSymbol *> NewTable(Table.size() * 2);
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NewTable.swap(Table);
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for (GdbSymbol *Sym : NewTable) {
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if (!Sym)
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continue;
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GdbSymbol **Slot = findSlot(Sym->NameHash, Sym->NameOffset);
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*Slot = Sym;
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}
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}
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// Methods finds a slot for symbol with given hash. The step size used to find
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// the next candidate slot when handling a hash collision is specified in
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// .gdb_index section format. The hash value for a table entry is computed by
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// applying an iterative hash function to the symbol's name.
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GdbSymbol **GdbHashTab::findSlot(uint32_t Hash, size_t Offset) {
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uint32_t Index = Hash & (Table.size() - 1);
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uint32_t Step = ((Hash * 17) & (Table.size() - 1)) | 1;
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for (;;) {
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GdbSymbol *S = Table[Index];
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if (!S || ((S->NameOffset == Offset) && (S->NameHash == Hash)))
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return &Table[Index];
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Index = (Index + Step) & (Table.size() - 1);
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}
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}
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template <class ELFT>
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static InputSectionBase<ELFT> *
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findSection(ArrayRef<InputSectionBase<ELFT> *> Arr, uint64_t Offset) {
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for (InputSectionBase<ELFT> *S : Arr)
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if (S && S != &InputSection<ELFT>::Discarded)
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if (Offset >= S->Offset && Offset < S->Offset + S->getSize())
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return S;
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return nullptr;
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}
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template <class ELFT>
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std::vector<AddressEntry<ELFT>>
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GdbIndexBuilder<ELFT>::readAddressArea(size_t CurrentCU) {
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std::vector<AddressEntry<ELFT>> Ret;
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for (const auto &CU : Dwarf->compile_units()) {
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DWARFAddressRangesVector Ranges;
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CU->collectAddressRanges(Ranges);
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ArrayRef<InputSectionBase<ELFT> *> Sections =
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DebugInfoSec->getFile()->getSections();
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for (std::pair<uint64_t, uint64_t> &R : Ranges)
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if (InputSectionBase<ELFT> *S = findSection(Sections, R.first))
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Ret.push_back(
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{S, R.first - S->Offset, R.second - S->Offset, CurrentCU});
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++CurrentCU;
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}
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return Ret;
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}
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// We return file offset as load address for allocatable sections. That is
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// currently used for collecting address ranges in readAddressArea(). We are
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// able then to find section index that range belongs to.
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template <class ELFT>
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uint64_t GdbIndexBuilder<ELFT>::getSectionLoadAddress(
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const object::SectionRef &Sec) const {
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if (static_cast<const ELFSectionRef &>(Sec).getFlags() & ELF::SHF_ALLOC)
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return static_cast<const ELFSectionRef &>(Sec).getOffset();
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return 0;
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}
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template <class ELFT>
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std::unique_ptr<LoadedObjectInfo> GdbIndexBuilder<ELFT>::clone() const {
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return {};
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}
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namespace lld {
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namespace elf {
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template class GdbIndexBuilder<ELF32LE>;
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template class GdbIndexBuilder<ELF32BE>;
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template class GdbIndexBuilder<ELF64LE>;
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template class GdbIndexBuilder<ELF64BE>;
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}
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}
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