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//===- tools/dsymutil/DwarfLinker.cpp - Dwarf debug info linker -----------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "DwarfLinker.h"
#include "BinaryHolder.h"
#include "DebugMap.h"
#include "DeclContext.h"
#include "DwarfStreamer.h"
#include "MachOUtils.h"
#include "NonRelocatableStringpool.h"
#include "dsymutil.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/IntervalMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Triple.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/CodeGen/AccelTable.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/DIE.h"
#include "llvm/Config/config.h"
#include "llvm/DebugInfo/DIContext.h"
#include "llvm/DebugInfo/DWARF/DWARFAbbreviationDeclaration.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/DebugInfo/DWARF/DWARFDataExtractor.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugLine.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugRangeList.h"
#include "llvm/DebugInfo/DWARF/DWARFDie.h"
#include "llvm/DebugInfo/DWARF/DWARFFormValue.h"
#include "llvm/DebugInfo/DWARF/DWARFSection.h"
#include "llvm/DebugInfo/DWARF/DWARFUnit.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCTargetOptions.h"
#include "llvm/Object/MachO.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Object/SymbolicFile.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/DJB.h"
#include "llvm/Support/DataExtractor.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/ThreadPool.h"
#include "llvm/Support/ToolOutputFile.h"
#include "llvm/Support/WithColor.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include <algorithm>
#include <cassert>
#include <cinttypes>
#include <climits>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <limits>
#include <map>
#include <memory>
#include <string>
#include <system_error>
#include <tuple>
#include <utility>
#include <vector>
namespace llvm {
namespace dsymutil {
/// Similar to DWARFUnitSection::getUnitForOffset(), but returning our
/// CompileUnit object instead.
static CompileUnit *getUnitForOffset(const UnitListTy &Units, uint64_t Offset) {
auto CU = std::upper_bound(
Units.begin(), Units.end(), Offset,
[](uint64_t LHS, const std::unique_ptr<CompileUnit> &RHS) {
return LHS < RHS->getOrigUnit().getNextUnitOffset();
return CU != Units.end() ? CU->get() : nullptr;
/// Resolve the DIE attribute reference that has been extracted in \p RefValue.
/// The resulting DIE might be in another CompileUnit which is stored into \p
/// ReferencedCU. \returns null if resolving fails for any reason.
static DWARFDie resolveDIEReference(const DwarfLinker &Linker,
const DebugMapObject &DMO,
const UnitListTy &Units,
const DWARFFormValue &RefValue,
const DWARFDie &DIE, CompileUnit *&RefCU) {
uint64_t RefOffset = *RefValue.getAsReference();
if ((RefCU = getUnitForOffset(Units, RefOffset)))
if (const auto RefDie = RefCU->getOrigUnit().getDIEForOffset(RefOffset)) {
// In a file with broken references, an attribute might point to a NULL
// DIE.
if (!RefDie.isNULL())
return RefDie;
Linker.reportWarning("could not find referenced DIE", DMO, &DIE);
return DWARFDie();
/// \returns whether the passed \a Attr type might contain a DIE reference
/// suitable for ODR uniquing.
static bool isODRAttribute(uint16_t Attr) {
switch (Attr) {
return false;
case dwarf::DW_AT_type:
case dwarf::DW_AT_containing_type:
case dwarf::DW_AT_specification:
case dwarf::DW_AT_abstract_origin:
case dwarf::DW_AT_import:
return true;
llvm_unreachable("Improper attribute.");
static bool isTypeTag(uint16_t Tag) {
switch (Tag) {
case dwarf::DW_TAG_array_type:
case dwarf::DW_TAG_class_type:
case dwarf::DW_TAG_enumeration_type:
case dwarf::DW_TAG_pointer_type:
case dwarf::DW_TAG_reference_type:
case dwarf::DW_TAG_string_type:
case dwarf::DW_TAG_structure_type:
case dwarf::DW_TAG_subroutine_type:
case dwarf::DW_TAG_typedef:
case dwarf::DW_TAG_union_type:
case dwarf::DW_TAG_ptr_to_member_type:
case dwarf::DW_TAG_set_type:
case dwarf::DW_TAG_subrange_type:
case dwarf::DW_TAG_base_type:
case dwarf::DW_TAG_const_type:
case dwarf::DW_TAG_constant:
case dwarf::DW_TAG_file_type:
case dwarf::DW_TAG_namelist:
case dwarf::DW_TAG_packed_type:
case dwarf::DW_TAG_volatile_type:
case dwarf::DW_TAG_restrict_type:
case dwarf::DW_TAG_atomic_type:
case dwarf::DW_TAG_interface_type:
case dwarf::DW_TAG_unspecified_type:
case dwarf::DW_TAG_shared_type:
return true;
return false;
bool DwarfLinker::DIECloner::getDIENames(const DWARFDie &Die,
AttributesInfo &Info,
OffsetsStringPool &StringPool,
bool StripTemplate) {
// This function will be called on DIEs having low_pcs and
// ranges. As getting the name might be more expansive, filter out
// blocks directly.
if (Die.getTag() == dwarf::DW_TAG_lexical_block)
return false;
// FIXME: a bit wasteful as the first getName might return the
// short name.
if (!Info.MangledName)
if (const char *MangledName = Die.getName(DINameKind::LinkageName))
Info.MangledName = StringPool.getEntry(MangledName);
if (!Info.Name)
if (const char *Name = Die.getName(DINameKind::ShortName))
Info.Name = StringPool.getEntry(Name);
if (StripTemplate && Info.Name && Info.MangledName != Info.Name) {
// FIXME: dsymutil compatibility. This is wrong for operator<
auto Split = Info.Name.getString().split('<');
if (!Split.second.empty())
Info.NameWithoutTemplate = StringPool.getEntry(Split.first);
return Info.Name || Info.MangledName;
/// Report a warning to the user, optionally including information about a
/// specific \p DIE related to the warning.
void DwarfLinker::reportWarning(const Twine &Warning, const DebugMapObject &DMO,
const DWARFDie *DIE) const {
StringRef Context = DMO.getObjectFilename();
warn(Warning, Context);
if (!Options.Verbose || !DIE)
DIDumpOptions DumpOpts;
DumpOpts.ChildRecurseDepth = 0;
DumpOpts.Verbose = Options.Verbose;
WithColor::note() << " in DIE:\n";
DIE->dump(errs(), 6 /* Indent */, DumpOpts);
bool DwarfLinker::createStreamer(const Triple &TheTriple,
raw_fd_ostream &OutFile) {
if (Options.NoOutput)
return true;
Streamer = std::make_unique<DwarfStreamer>(OutFile, Options);
return Streamer->init(TheTriple);
/// Resolve the relative path to a build artifact referenced by DWARF by
/// applying DW_AT_comp_dir.
static void resolveRelativeObjectPath(SmallVectorImpl<char> &Buf, DWARFDie CU) {
sys::path::append(Buf, dwarf::toString(CU.find(dwarf::DW_AT_comp_dir), ""));
/// Collect references to parseable Swift interfaces in imported
/// DW_TAG_module blocks.
static void analyzeImportedModule(
const DWARFDie &DIE, CompileUnit &CU,
std::map<std::string, std::string> &ParseableSwiftInterfaces,
std::function<void(const Twine &, const DWARFDie &)> ReportWarning) {
if (CU.getLanguage() != dwarf::DW_LANG_Swift)
StringRef Path = dwarf::toStringRef(DIE.find(dwarf::DW_AT_LLVM_include_path));
if (!Path.endswith(".swiftinterface"))
if (Optional<DWARFFormValue> Val = DIE.find(dwarf::DW_AT_name))
if (Optional<const char *> Name = Val->getAsCString()) {
auto &Entry = ParseableSwiftInterfaces[*Name];
// The prepend path is applied later when copying.
DWARFDie CUDie = CU.getOrigUnit().getUnitDIE();
SmallString<128> ResolvedPath;
if (sys::path::is_relative(Path))
resolveRelativeObjectPath(ResolvedPath, CUDie);
sys::path::append(ResolvedPath, Path);
if (!Entry.empty() && Entry != ResolvedPath)
Twine("Conflicting parseable interfaces for Swift Module ") +
*Name + ": " + Entry + " and " + Path,
Entry = ResolvedPath.str();
/// Recursive helper to build the global DeclContext information and
/// gather the child->parent relationships in the original compile unit.
/// \return true when this DIE and all of its children are only
/// forward declarations to types defined in external clang modules
/// (i.e., forward declarations that are children of a DW_TAG_module).
static bool analyzeContextInfo(
const DWARFDie &DIE, unsigned ParentIdx, CompileUnit &CU,
DeclContext *CurrentDeclContext, UniquingStringPool &StringPool,
DeclContextTree &Contexts, uint64_t ModulesEndOffset,
std::map<std::string, std::string> &ParseableSwiftInterfaces,
std::function<void(const Twine &, const DWARFDie &)> ReportWarning,
bool InImportedModule = false) {
unsigned MyIdx = CU.getOrigUnit().getDIEIndex(DIE);
CompileUnit::DIEInfo &Info = CU.getInfo(MyIdx);
// Clang imposes an ODR on modules(!) regardless of the language:
// "The module-id should consist of only a single identifier,
// which provides the name of the module being defined. Each
// module shall have a single definition."
// This does not extend to the types inside the modules:
// "[I]n C, this implies that if two structs are defined in
// different submodules with the same name, those two types are
// distinct types (but may be compatible types if their
// definitions match)."
// We treat non-C++ modules like namespaces for this reason.
if (DIE.getTag() == dwarf::DW_TAG_module && ParentIdx == 0 &&
dwarf::toString(DIE.find(dwarf::DW_AT_name), "") !=
CU.getClangModuleName()) {
InImportedModule = true;
analyzeImportedModule(DIE, CU, ParseableSwiftInterfaces, ReportWarning);
Info.ParentIdx = ParentIdx;
bool InClangModule = CU.isClangModule() || InImportedModule;
if (CU.hasODR() || InClangModule) {
if (CurrentDeclContext) {
auto PtrInvalidPair = Contexts.getChildDeclContext(
*CurrentDeclContext, DIE, CU, StringPool, InClangModule);
CurrentDeclContext = PtrInvalidPair.getPointer();
Info.Ctxt =
PtrInvalidPair.getInt() ? nullptr : PtrInvalidPair.getPointer();
if (Info.Ctxt)
} else
Info.Ctxt = CurrentDeclContext = nullptr;
Info.Prune = InImportedModule;
if (DIE.hasChildren())
for (auto Child : DIE.children())
Info.Prune &= analyzeContextInfo(Child, MyIdx, CU, CurrentDeclContext,
StringPool, Contexts, ModulesEndOffset,
ParseableSwiftInterfaces, ReportWarning,
// Prune this DIE if it is either a forward declaration inside a
// DW_TAG_module or a DW_TAG_module that contains nothing but
// forward declarations.
Info.Prune &= (DIE.getTag() == dwarf::DW_TAG_module) ||
(isTypeTag(DIE.getTag()) &&
dwarf::toUnsigned(DIE.find(dwarf::DW_AT_declaration), 0));
// Only prune forward declarations inside a DW_TAG_module for which a
// definition exists elsewhere.
if (ModulesEndOffset == 0)
Info.Prune &= Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset();
Info.Prune &= Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset() > 0 &&
Info.Ctxt->getCanonicalDIEOffset() <= ModulesEndOffset;
return Info.Prune;
} // namespace dsymutil
static bool dieNeedsChildrenToBeMeaningful(uint32_t Tag) {
switch (Tag) {
return false;
case dwarf::DW_TAG_subprogram:
case dwarf::DW_TAG_lexical_block:
case dwarf::DW_TAG_subroutine_type:
case dwarf::DW_TAG_structure_type:
case dwarf::DW_TAG_class_type:
case dwarf::DW_TAG_union_type:
return true;
llvm_unreachable("Invalid Tag");
void DwarfLinker::startDebugObject(LinkContext &Context) {
// Iterate over the debug map entries and put all the ones that are
// functions (because they have a size) into the Ranges map. This map is
// very similar to the FunctionRanges that are stored in each unit, with 2
// notable differences:
// 1. Obviously this one is global, while the other ones are per-unit.
// 2. This one contains not only the functions described in the DIE
// tree, but also the ones that are only in the debug map.
// The latter information is required to reproduce dsymutil's logic while
// linking line tables. The cases where this information matters look like
// bugs that need to be investigated, but for now we need to reproduce
// dsymutil's behavior.
// FIXME: Once we understood exactly if that information is needed,
// maybe totally remove this (or try to use it to do a real
// -gline-tables-only on Darwin.
for (const auto &Entry : Context.DMO.symbols()) {
const auto &Mapping = Entry.getValue();
if (Mapping.Size && Mapping.ObjectAddress)
Context.Ranges[*Mapping.ObjectAddress] = DebugMapObjectRange(
*Mapping.ObjectAddress + Mapping.Size,
int64_t(Mapping.BinaryAddress) - *Mapping.ObjectAddress);
void DwarfLinker::endDebugObject(LinkContext &Context) {
for (auto I = DIEBlocks.begin(), E = DIEBlocks.end(); I != E; ++I)
for (auto I = DIELocs.begin(), E = DIELocs.end(); I != E; ++I)
static bool isMachOPairedReloc(uint64_t RelocType, uint64_t Arch) {
switch (Arch) {
case Triple::x86:
return RelocType == MachO::GENERIC_RELOC_SECTDIFF ||
case Triple::x86_64:
return RelocType == MachO::X86_64_RELOC_SUBTRACTOR;
case Triple::arm:
case Triple::thumb:
return RelocType == MachO::ARM_RELOC_SECTDIFF ||
RelocType == MachO::ARM_RELOC_HALF ||
case Triple::aarch64:
return RelocType == MachO::ARM64_RELOC_SUBTRACTOR;
return false;
/// Iterate over the relocations of the given \p Section and
/// store the ones that correspond to debug map entries into the
/// ValidRelocs array.
void DwarfLinker::RelocationManager::findValidRelocsMachO(
const object::SectionRef &Section, const object::MachOObjectFile &Obj,
const DebugMapObject &DMO) {
Expected<StringRef> ContentsOrErr = Section.getContents();
if (!ContentsOrErr) {
Linker.reportWarning("error reading section", DMO);
DataExtractor Data(*ContentsOrErr, Obj.isLittleEndian(), 0);
bool SkipNext = false;
for (const object::RelocationRef &Reloc : Section.relocations()) {
if (SkipNext) {
SkipNext = false;
object::DataRefImpl RelocDataRef = Reloc.getRawDataRefImpl();
MachO::any_relocation_info MachOReloc = Obj.getRelocation(RelocDataRef);
if (isMachOPairedReloc(Obj.getAnyRelocationType(MachOReloc),
Obj.getArch())) {
SkipNext = true;
Linker.reportWarning("unsupported relocation in debug_info section.",
unsigned RelocSize = 1 << Obj.getAnyRelocationLength(MachOReloc);
uint64_t Offset64 = Reloc.getOffset();
if ((RelocSize != 4 && RelocSize != 8)) {
Linker.reportWarning("unsupported relocation in debug_info section.",
uint64_t OffsetCopy = Offset64;
// Mach-o uses REL relocations, the addend is at the relocation offset.
uint64_t Addend = Data.getUnsigned(&OffsetCopy, RelocSize);
uint64_t SymAddress;
int64_t SymOffset;
if (Obj.isRelocationScattered(MachOReloc)) {
// The address of the base symbol for scattered relocations is
// stored in the reloc itself. The actual addend will store the
// base address plus the offset.
SymAddress = Obj.getScatteredRelocationValue(MachOReloc);
SymOffset = int64_t(Addend) - SymAddress;
} else {
SymAddress = Addend;
SymOffset = 0;
auto Sym = Reloc.getSymbol();
if (Sym != Obj.symbol_end()) {
Expected<StringRef> SymbolName = Sym->getName();
if (!SymbolName) {
Linker.reportWarning("error getting relocation symbol name.", DMO);
if (const auto *Mapping = DMO.lookupSymbol(*SymbolName))
ValidRelocs.emplace_back(Offset64, RelocSize, Addend, Mapping);
} else if (const auto *Mapping = DMO.lookupObjectAddress(SymAddress)) {
// Do not store the addend. The addend was the address of the symbol in
// the object file, the address in the binary that is stored in the debug
// map doesn't need to be offset.
ValidRelocs.emplace_back(Offset64, RelocSize, SymOffset, Mapping);
/// Dispatch the valid relocation finding logic to the
/// appropriate handler depending on the object file format.
bool DwarfLinker::RelocationManager::findValidRelocs(
const object::SectionRef &Section, const object::ObjectFile &Obj,
const DebugMapObject &DMO) {
// Dispatch to the right handler depending on the file type.
if (auto *MachOObj = dyn_cast<object::MachOObjectFile>(&Obj))
findValidRelocsMachO(Section, *MachOObj, DMO);
Twine("unsupported object file type: ") + Obj.getFileName(), DMO);
if (ValidRelocs.empty())
return false;
// Sort the relocations by offset. We will walk the DIEs linearly in
// the file, this allows us to just keep an index in the relocation
// array that we advance during our walk, rather than resorting to
// some associative container. See DwarfLinker::NextValidReloc.
return true;
/// Look for relocations in the debug_info section that match
/// entries in the debug map. These relocations will drive the Dwarf
/// link by indicating which DIEs refer to symbols present in the
/// linked binary.
/// \returns whether there are any valid relocations in the debug info.
bool DwarfLinker::RelocationManager::findValidRelocsInDebugInfo(
const object::ObjectFile &Obj, const DebugMapObject &DMO) {
// Find the debug_info section.
for (const object::SectionRef &Section : Obj.sections()) {
StringRef SectionName;
if (Expected<StringRef> NameOrErr = Section.getName())
SectionName = *NameOrErr;
SectionName = SectionName.substr(SectionName.find_first_not_of("._"));
if (SectionName != "debug_info")
return findValidRelocs(Section, Obj, DMO);
return false;
/// Checks that there is a relocation against an actual debug
/// map entry between \p StartOffset and \p NextOffset.
/// This function must be called with offsets in strictly ascending
/// order because it never looks back at relocations it already 'went past'.
/// \returns true and sets Info.InDebugMap if it is the case.
bool DwarfLinker::RelocationManager::hasValidRelocation(
uint64_t StartOffset, uint64_t EndOffset, CompileUnit::DIEInfo &Info) {
assert(NextValidReloc == 0 ||
StartOffset > ValidRelocs[NextValidReloc - 1].Offset);
if (NextValidReloc >= ValidRelocs.size())
return false;
uint64_t RelocOffset = ValidRelocs[NextValidReloc].Offset;
// We might need to skip some relocs that we didn't consider. For
// example the high_pc of a discarded DIE might contain a reloc that
// is in the list because it actually corresponds to the start of a
// function that is in the debug map.
while (RelocOffset < StartOffset && NextValidReloc < ValidRelocs.size() - 1)
RelocOffset = ValidRelocs[++NextValidReloc].Offset;
if (RelocOffset < StartOffset || RelocOffset >= EndOffset)
return false;
const auto &ValidReloc = ValidRelocs[NextValidReloc++];
const auto &Mapping = ValidReloc.Mapping->getValue();
const uint64_t BinaryAddress = Mapping.BinaryAddress;
const uint64_t ObjectAddress = Mapping.ObjectAddress
? uint64_t(*Mapping.ObjectAddress)
: std::numeric_limits<uint64_t>::max();
if (Linker.Options.Verbose)
outs() << "Found valid debug map entry: " << ValidReloc.Mapping->getKey()
<< "\t"
<< format("0x%016" PRIx64 " => 0x%016" PRIx64 "\n", ObjectAddress,
Info.AddrAdjust = BinaryAddress + ValidReloc.Addend;
if (Mapping.ObjectAddress)
Info.AddrAdjust -= ObjectAddress;
Info.InDebugMap = true;
return true;
/// Get the starting and ending (exclusive) offset for the
/// attribute with index \p Idx descibed by \p Abbrev. \p Offset is
/// supposed to point to the position of the first attribute described
/// by \p Abbrev.
/// \return [StartOffset, EndOffset) as a pair.
static std::pair<uint64_t, uint64_t>
getAttributeOffsets(const DWARFAbbreviationDeclaration *Abbrev, unsigned Idx,
uint64_t Offset, const DWARFUnit &Unit) {
DataExtractor Data = Unit.getDebugInfoExtractor();
for (unsigned i = 0; i < Idx; ++i)
DWARFFormValue::skipValue(Abbrev->getFormByIndex(i), Data, &Offset,
uint64_t End = Offset;
DWARFFormValue::skipValue(Abbrev->getFormByIndex(Idx), Data, &End,
return std::make_pair(Offset, End);
/// Check if a variable describing DIE should be kept.
/// \returns updated TraversalFlags.
unsigned DwarfLinker::shouldKeepVariableDIE(RelocationManager &RelocMgr,
const DWARFDie &DIE,
CompileUnit &Unit,
CompileUnit::DIEInfo &MyInfo,
unsigned Flags) {
const auto *Abbrev = DIE.getAbbreviationDeclarationPtr();
// Global variables with constant value can always be kept.
if (!(Flags & TF_InFunctionScope) &&
Abbrev->findAttributeIndex(dwarf::DW_AT_const_value)) {
MyInfo.InDebugMap = true;
return Flags | TF_Keep;
Optional<uint32_t> LocationIdx =
if (!LocationIdx)
return Flags;
uint64_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
const DWARFUnit &OrigUnit = Unit.getOrigUnit();
uint64_t LocationOffset, LocationEndOffset;
std::tie(LocationOffset, LocationEndOffset) =
getAttributeOffsets(Abbrev, *LocationIdx, Offset, OrigUnit);
// See if there is a relocation to a valid debug map entry inside
// this variable's location. The order is important here. We want to
// always check if the variable has a valid relocation, so that the
// DIEInfo is filled. However, we don't want a static variable in a
// function to force us to keep the enclosing function.
if (!RelocMgr.hasValidRelocation(LocationOffset, LocationEndOffset, MyInfo) ||
(Flags & TF_InFunctionScope))
return Flags;
if (Options.Verbose) {
outs() << "Keeping variable DIE:";
DIDumpOptions DumpOpts;
DumpOpts.ChildRecurseDepth = 0;
DumpOpts.Verbose = Options.Verbose;
DIE.dump(outs(), 8 /* Indent */, DumpOpts);
return Flags | TF_Keep;
/// Check if a function describing DIE should be kept.
/// \returns updated TraversalFlags.
unsigned DwarfLinker::shouldKeepSubprogramDIE(
RelocationManager &RelocMgr, RangesTy &Ranges, const DWARFDie &DIE,
const DebugMapObject &DMO, CompileUnit &Unit, CompileUnit::DIEInfo &MyInfo,
unsigned Flags) {
const auto *Abbrev = DIE.getAbbreviationDeclarationPtr();
Flags |= TF_InFunctionScope;
Optional<uint32_t> LowPcIdx = Abbrev->findAttributeIndex(dwarf::DW_AT_low_pc);
if (!LowPcIdx)
return Flags;
uint64_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
DWARFUnit &OrigUnit = Unit.getOrigUnit();
uint64_t LowPcOffset, LowPcEndOffset;
std::tie(LowPcOffset, LowPcEndOffset) =
getAttributeOffsets(Abbrev, *LowPcIdx, Offset, OrigUnit);
auto LowPc = dwarf::toAddress(DIE.find(dwarf::DW_AT_low_pc));
assert(LowPc.hasValue() && "low_pc attribute is not an address.");
if (!LowPc ||
!RelocMgr.hasValidRelocation(LowPcOffset, LowPcEndOffset, MyInfo))
return Flags;
if (Options.Verbose) {
outs() << "Keeping subprogram DIE:";
DIDumpOptions DumpOpts;
DumpOpts.ChildRecurseDepth = 0;
DumpOpts.Verbose = Options.Verbose;
DIE.dump(outs(), 8 /* Indent */, DumpOpts);
if (DIE.getTag() == dwarf::DW_TAG_label) {
if (Unit.hasLabelAt(*LowPc))
return Flags;
// FIXME: dsymutil-classic compat. dsymutil-classic doesn't consider labels
// that don't fall into the CU's aranges. This is wrong IMO. Debug info
// generation bugs aside, this is really wrong in the case of labels, where
// a label marking the end of a function will have a PC == CU's high_pc.
if (dwarf::toAddress(OrigUnit.getUnitDIE().find(dwarf::DW_AT_high_pc))
.getValueOr(UINT64_MAX) <= LowPc)
return Flags;
Unit.addLabelLowPc(*LowPc, MyInfo.AddrAdjust);
return Flags | TF_Keep;
Flags |= TF_Keep;
Optional<uint64_t> HighPc = DIE.getHighPC(*LowPc);
if (!HighPc) {
reportWarning("Function without high_pc. Range will be discarded.\n", DMO,
return Flags;
// Replace the debug map range with a more accurate one.
Ranges[*LowPc] = DebugMapObjectRange(*HighPc, MyInfo.AddrAdjust);
Unit.addFunctionRange(*LowPc, *HighPc, MyInfo.AddrAdjust);
return Flags;
/// Check if a DIE should be kept.
/// \returns updated TraversalFlags.
unsigned DwarfLinker::shouldKeepDIE(RelocationManager &RelocMgr,
RangesTy &Ranges, const DWARFDie &DIE,
const DebugMapObject &DMO,
CompileUnit &Unit,
CompileUnit::DIEInfo &MyInfo,
unsigned Flags) {
switch (DIE.getTag()) {
case dwarf::DW_TAG_constant:
case dwarf::DW_TAG_variable:
return shouldKeepVariableDIE(RelocMgr, DIE, Unit, MyInfo, Flags);
case dwarf::DW_TAG_subprogram:
case dwarf::DW_TAG_label:
return shouldKeepSubprogramDIE(RelocMgr, Ranges, DIE, DMO, Unit, MyInfo,
case dwarf::DW_TAG_base_type:
// DWARF Expressions may reference basic types, but scanning them
// is expensive. Basic types are tiny, so just keep all of them.
case dwarf::DW_TAG_imported_module:
case dwarf::DW_TAG_imported_declaration:
case dwarf::DW_TAG_imported_unit:
// We always want to keep these.
return Flags | TF_Keep;
return Flags;
/// Mark the passed DIE as well as all the ones it depends on
/// as kept.
/// This function is called by lookForDIEsToKeep on DIEs that are
/// newly discovered to be needed in the link. It recursively calls
/// back to lookForDIEsToKeep while adding TF_DependencyWalk to the
/// TraversalFlags to inform it that it's not doing the primary DIE
/// tree walk.
void DwarfLinker::keepDIEAndDependencies(
RelocationManager &RelocMgr, RangesTy &Ranges, const UnitListTy &Units,
const DWARFDie &Die, CompileUnit::DIEInfo &MyInfo,
const DebugMapObject &DMO, CompileUnit &CU, bool UseODR) {
DWARFUnit &Unit = CU.getOrigUnit();
MyInfo.Keep = true;
// We're looking for incomplete types.
MyInfo.Incomplete = Die.getTag() != dwarf::DW_TAG_subprogram &&
Die.getTag() != dwarf::DW_TAG_member &&
dwarf::toUnsigned(Die.find(dwarf::DW_AT_declaration), 0);
// First mark all the parent chain as kept.
unsigned AncestorIdx = MyInfo.ParentIdx;
while (!CU.getInfo(AncestorIdx).Keep) {
unsigned ODRFlag = UseODR ? TF_ODR : 0;
lookForDIEsToKeep(RelocMgr, Ranges, Units, Unit.getDIEAtIndex(AncestorIdx),
TF_ParentWalk | TF_Keep | TF_DependencyWalk | ODRFlag);
AncestorIdx = CU.getInfo(AncestorIdx).ParentIdx;
// Then we need to mark all the DIEs referenced by this DIE's
// attributes as kept.
DWARFDataExtractor Data = Unit.getDebugInfoExtractor();
const auto *Abbrev = Die.getAbbreviationDeclarationPtr();
uint64_t Offset = Die.getOffset() + getULEB128Size(Abbrev->getCode());
// Mark all DIEs referenced through attributes as kept.
for (const auto &AttrSpec : Abbrev->attributes()) {
DWARFFormValue Val(AttrSpec.Form);
if (!Val.isFormClass(DWARFFormValue::FC_Reference) ||
AttrSpec.Attr == dwarf::DW_AT_sibling) {
DWARFFormValue::skipValue(AttrSpec.Form, Data, &Offset,
Val.extractValue(Data, &Offset, Unit.getFormParams(), &Unit);
CompileUnit *ReferencedCU;
if (auto RefDie =
resolveDIEReference(*this, DMO, Units, Val, Die, ReferencedCU)) {
uint32_t RefIdx = ReferencedCU->getOrigUnit().getDIEIndex(RefDie);
CompileUnit::DIEInfo &Info = ReferencedCU->getInfo(RefIdx);
bool IsModuleRef = Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset() &&
// If the referenced DIE has a DeclContext that has already been
// emitted, then do not keep the one in this CU. We'll link to
// the canonical DIE in cloneDieReferenceAttribute.
// FIXME: compatibility with dsymutil-classic. UseODR shouldn't
// be necessary and could be advantageously replaced by
// ReferencedCU->hasODR() && CU.hasODR().
// FIXME: compatibility with dsymutil-classic. There is no
// reason not to unique ref_addr references.
if (AttrSpec.Form != dwarf::DW_FORM_ref_addr && (UseODR || IsModuleRef) &&
Info.Ctxt &&
Info.Ctxt != ReferencedCU->getInfo(Info.ParentIdx).Ctxt &&
Info.Ctxt->getCanonicalDIEOffset() && isODRAttribute(AttrSpec.Attr))
// Keep a module forward declaration if there is no definition.
if (!(isODRAttribute(AttrSpec.Attr) && Info.Ctxt &&
Info.Prune = false;
unsigned ODRFlag = UseODR ? TF_ODR : 0;
lookForDIEsToKeep(RelocMgr, Ranges, Units, RefDie, DMO, *ReferencedCU,
TF_Keep | TF_DependencyWalk | ODRFlag);
// The incomplete property is propagated if the current DIE is complete
// but references an incomplete DIE.
if (Info.Incomplete && !MyInfo.Incomplete &&
(Die.getTag() == dwarf::DW_TAG_typedef ||
Die.getTag() == dwarf::DW_TAG_member ||
Die.getTag() == dwarf::DW_TAG_reference_type ||
Die.getTag() == dwarf::DW_TAG_ptr_to_member_type ||
Die.getTag() == dwarf::DW_TAG_pointer_type))
MyInfo.Incomplete = true;
namespace {
/// This class represents an item in the work list. In addition to it's obvious
/// purpose of representing the state associated with a particular run of the
/// work loop, it also serves as a marker to indicate that we should run the
/// "continuation" code.
/// Originally, the latter was lambda which allowed arbitrary code to be run.
/// Because we always need to run the exact same code, it made more sense to
/// use a boolean and repurpose the already existing DIE field.
struct WorklistItem {
unsigned Flags;
bool IsContinuation;
CompileUnit::DIEInfo *ChildInfo = nullptr;
/// Construct a classic worklist item.
WorklistItem(DWARFDie Die, unsigned Flags)
: Die(Die), Flags(Flags), IsContinuation(false){};
/// Creates a continuation marker.
WorklistItem(DWARFDie Die) : Die(Die), IsContinuation(true){};
} // namespace
// Helper that updates the completeness of the current DIE. It depends on the
// fact that the incompletness of its children is already computed.
static void updateIncompleteness(const DWARFDie &Die,
CompileUnit::DIEInfo &ChildInfo,
CompileUnit &CU) {
// Only propagate incomplete members.
if (Die.getTag() != dwarf::DW_TAG_structure_type &&
Die.getTag() != dwarf::DW_TAG_class_type)
unsigned Idx = CU.getOrigUnit().getDIEIndex(Die);
CompileUnit::DIEInfo &MyInfo = CU.getInfo(Idx);
if (MyInfo.Incomplete)
if (ChildInfo.Incomplete || ChildInfo.Prune)
MyInfo.Incomplete = true;
/// Recursively walk the \p DIE tree and look for DIEs to
/// keep. Store that information in \p CU's DIEInfo.
/// This function is the entry point of the DIE selection
/// algorithm. It is expected to walk the DIE tree in file order and
/// (though the mediation of its helper) call hasValidRelocation() on
/// each DIE that might be a 'root DIE' (See DwarfLinker class
/// comment).
/// While walking the dependencies of root DIEs, this function is
/// also called, but during these dependency walks the file order is
/// not respected. The TF_DependencyWalk flag tells us which kind of
/// traversal we are currently doing.
/// The return value indicates whether the DIE is incomplete.
void DwarfLinker::lookForDIEsToKeep(RelocationManager &RelocMgr,
RangesTy &Ranges, const UnitListTy &Units,
const DWARFDie &Die,
const DebugMapObject &DMO, CompileUnit &CU,
unsigned Flags) {
// LIFO work list.
SmallVector<WorklistItem, 4> Worklist;
Worklist.emplace_back(Die, Flags);
while (!Worklist.empty()) {
WorklistItem Current = Worklist.back();
if (Current.IsContinuation) {
updateIncompleteness(Current.Die, *Current.ChildInfo, CU);
unsigned Idx = CU.getOrigUnit().getDIEIndex(Current.Die);
CompileUnit::DIEInfo &MyInfo = CU.getInfo(Idx);
// At this point we are guaranteed to have a continuation marker before us
// in the worklist, except for the last DIE.
if (!Worklist.empty())
Worklist.back().ChildInfo = &MyInfo;
if (MyInfo.Prune)
// If the Keep flag is set, we are marking a required DIE's dependencies.
// If our target is already marked as kept, we're all set.
bool AlreadyKept = MyInfo.Keep;
if ((Current.Flags & TF_DependencyWalk) && AlreadyKept)
// We must not call shouldKeepDIE while called from keepDIEAndDependencies,
// because it would screw up the relocation finding logic.
if (!(Current.Flags & TF_DependencyWalk))
Current.Flags = shouldKeepDIE(RelocMgr, Ranges, Current.Die, DMO, CU,
MyInfo, Current.Flags);
// If it is a newly kept DIE mark it as well as all its dependencies as
// kept.
if (!AlreadyKept && (Current.Flags & TF_Keep)) {
bool UseOdr = (Current.Flags & TF_DependencyWalk)
? (Current.Flags & TF_ODR)
: CU.hasODR();
keepDIEAndDependencies(RelocMgr, Ranges, Units, Current.Die, MyInfo, DMO,
CU, UseOdr);
// The TF_ParentWalk flag tells us that we are currently walking up
// the parent chain of a required DIE, and we don't want to mark all
// the children of the parents as kept (consider for example a
// DW_TAG_namespace node in the parent chain). There are however a
// set of DIE types for which we want to ignore that directive and still
// walk their children.
if (dieNeedsChildrenToBeMeaningful(Current.Die.getTag()))
Current.Flags &= ~TF_ParentWalk;
if (!Current.Die.hasChildren() || (Current.Flags & TF_ParentWalk))
// Add children in reverse order to the worklist to effectively process
// them in order.
for (auto Child : reverse(Current.Die.children())) {
// Add continuation marker before every child to calculate incompleteness
// after the last child is processed. We can't store this information in
// the same item because we might have to process other continuations
// first.
Worklist.emplace_back(Child, Current.Flags);
/// Assign an abbreviation number to \p Abbrev.
/// Our DIEs get freed after every DebugMapObject has been processed,
/// thus the FoldingSet we use to unique DIEAbbrevs cannot refer to
/// the instances hold by the DIEs. When we encounter an abbreviation
/// that we don't know, we create a permanent copy of it.
void DwarfLinker::AssignAbbrev(DIEAbbrev &Abbrev) {
// Check the set for priors.
FoldingSetNodeID ID;
void *InsertToken;
DIEAbbrev *InSet = AbbreviationsSet.FindNodeOrInsertPos(ID, InsertToken);
// If it's newly added.
if (InSet) {
// Assign existing abbreviation number.
} else {
// Add to abbreviation list.
std::make_unique<DIEAbbrev>(Abbrev.getTag(), Abbrev.hasChildren()));
for (const auto &Attr : Abbrev.getData())
Abbreviations.back()->AddAttribute(Attr.getAttribute(), Attr.getForm());
AbbreviationsSet.InsertNode(Abbreviations.back().get(), InsertToken);
// Assign the unique abbreviation number.
unsigned DwarfLinker::DIECloner::cloneStringAttribute(
DIE &Die, AttributeSpec AttrSpec, const DWARFFormValue &Val,
const DWARFUnit &U, OffsetsStringPool &StringPool, AttributesInfo &Info) {
// Switch everything to out of line strings.
const char *String = *Val.getAsCString();
auto StringEntry = StringPool.getEntry(String);
// Update attributes info.
if (AttrSpec.Attr == dwarf::DW_AT_name)
Info.Name = StringEntry;
else if (AttrSpec.Attr == dwarf::DW_AT_MIPS_linkage_name ||
AttrSpec.Attr == dwarf::DW_AT_linkage_name)
Info.MangledName = StringEntry;
Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr), dwarf::DW_FORM_strp,
return 4;
unsigned DwarfLinker::DIECloner::cloneDieReferenceAttribute(
DIE &Die, const DWARFDie &InputDIE, AttributeSpec AttrSpec,
unsigned AttrSize, const DWARFFormValue &Val, const DebugMapObject &DMO,
CompileUnit &Unit) {
const DWARFUnit &U = Unit.getOrigUnit();
uint64_t Ref = *Val.getAsReference();
DIE *NewRefDie = nullptr;
CompileUnit *RefUnit = nullptr;
DeclContext *Ctxt = nullptr;
DWARFDie RefDie =
resolveDIEReference(Linker, DMO, CompileUnits, Val, InputDIE, RefUnit);
// If the referenced DIE is not found, drop the attribute.
if (!RefDie || AttrSpec.Attr == dwarf::DW_AT_sibling)
return 0;
unsigned Idx = RefUnit->getOrigUnit().getDIEIndex(RefDie);
CompileUnit::DIEInfo &RefInfo = RefUnit->getInfo(Idx);
// If we already have emitted an equivalent DeclContext, just point
// at it.
if (isODRAttribute(AttrSpec.Attr)) {
Ctxt = RefInfo.Ctxt;
if (Ctxt && Ctxt->getCanonicalDIEOffset()) {
DIEInteger Attr(Ctxt->getCanonicalDIEOffset());
Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
dwarf::DW_FORM_ref_addr, Attr);
return U.getRefAddrByteSize();
if (!RefInfo.Clone) {
assert(Ref > InputDIE.getOffset());
// We haven't cloned this DIE yet. Just create an empty one and
// store it. It'll get really cloned when we process it.
RefInfo.Clone = DIE::get(DIEAlloc, dwarf::Tag(RefDie.getTag()));
NewRefDie = RefInfo.Clone;
if (AttrSpec.Form == dwarf::DW_FORM_ref_addr ||
(Unit.hasODR() && isODRAttribute(AttrSpec.Attr))) {
// We cannot currently rely on a DIEEntry to emit ref_addr
// references, because the implementation calls back to DwarfDebug
// to find the unit offset. (We don't have a DwarfDebug)
// FIXME: we should be able to design DIEEntry reliance on
// DwarfDebug away.
uint64_t Attr;
if (Ref < InputDIE.getOffset()) {
// We must have already cloned that DIE.
uint32_t NewRefOffset =
RefUnit->getStartOffset() + NewRefDie->getOffset();
Attr = NewRefOffset;
Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
dwarf::DW_FORM_ref_addr, DIEInteger(Attr));
} else {
// A forward reference. Note and fixup later.
Attr = 0xBADDEF;
NewRefDie, RefUnit, Ctxt,
Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
dwarf::DW_FORM_ref_addr, DIEInteger(Attr)));
return U.getRefAddrByteSize();
Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
dwarf::Form(AttrSpec.Form), DIEEntry(*NewRefDie));
return AttrSize;
void DwarfLinker::DIECloner::cloneExpression(
DataExtractor &Data, DWARFExpression Expression, const DebugMapObject &DMO,
CompileUnit &Unit, SmallVectorImpl<uint8_t> &OutputBuffer) {
using Encoding = DWARFExpression::Operation::Encoding;
uint64_t OpOffset = 0;
for (auto &Op : Expression) {
auto Description = Op.getDescription();
// DW_OP_const_type is variable-length and has 3
// operands. DWARFExpression thus far only supports 2.
auto Op0 = Description.Op[0];
auto Op1 = Description.Op[1];
if ((Op0 == Encoding::BaseTypeRef && Op1 != Encoding::SizeNA) ||
(Op1 == Encoding::BaseTypeRef && Op0 != Encoding::Size1))
Linker.reportWarning("Unsupported DW_OP encoding.", DMO);
if ((Op0 == Encoding::BaseTypeRef && Op1 == Encoding::SizeNA) ||
(Op1 == Encoding::BaseTypeRef && Op0 == Encoding::Size1)) {
// This code assumes that the other non-typeref operand fits into 1 byte.
assert(OpOffset < Op.getEndOffset());
uint32_t ULEBsize = Op.getEndOffset() - OpOffset - 1;
assert(ULEBsize <= 16);
// Copy over the operation.
uint64_t RefOffset;
if (Op1 == Encoding::SizeNA) {
RefOffset = Op.getRawOperand(0);
} else {
RefOffset = Op.getRawOperand(1);
auto RefDie = Unit.getOrigUnit().getDIEForOffset(RefOffset);
uint32_t RefIdx = Unit.getOrigUnit().getDIEIndex(RefDie);
CompileUnit::DIEInfo &Info = Unit.getInfo(RefIdx);
uint32_t Offset = 0;
if (DIE *Clone = Info.Clone)
Offset = Clone->getOffset();
Linker.reportWarning("base type ref doesn't point to DW_TAG_base_type.",
uint8_t ULEB[16];
unsigned RealSize = encodeULEB128(Offset, ULEB, ULEBsize);
if (RealSize > ULEBsize) {
// Emit the generic type as a fallback.
RealSize = encodeULEB128(0, ULEB, ULEBsize);
Linker.reportWarning("base type ref doesn't fit.", DMO);
assert(RealSize == ULEBsize && "padding failed");
ArrayRef<uint8_t> ULEBbytes(ULEB, ULEBsize);
OutputBuffer.append(ULEBbytes.begin(), ULEBbytes.end());
} else {
// Copy over everything else unmodified.
StringRef Bytes = Data.getData().slice(OpOffset, Op.getEndOffset());
OutputBuffer.append(Bytes.begin(), Bytes.end());
OpOffset = Op.getEndOffset();
unsigned DwarfLinker::DIECloner::cloneBlockAttribute(
DIE &Die, const DebugMapObject &DMO, CompileUnit &Unit,
AttributeSpec AttrSpec, const DWARFFormValue &Val, unsigned AttrSize,
bool IsLittleEndian) {
DIEValueList *Attr;
DIEValue Value;
DIELoc *Loc = nullptr;
DIEBlock *Block = nullptr;
if (AttrSpec.Form == dwarf::DW_FORM_exprloc) {
Loc = new (DIEAlloc) DIELoc;
} else {
Block = new (DIEAlloc) DIEBlock;
Attr = Loc ? static_cast<DIEValueList *>(Loc)
: static_cast<DIEValueList *>(Block);
if (Loc)
Value = DIEValue(dwarf::Attribute(AttrSpec.Attr),
dwarf::Form(AttrSpec.Form), Loc);
Value = DIEValue(dwarf::Attribute(AttrSpec.Attr),
dwarf::Form(AttrSpec.Form), Block);
// If the block is a DWARF Expression, clone it into the temporary
// buffer using cloneExpression(), otherwise copy the data directly.
SmallVector<uint8_t, 32> Buffer;
ArrayRef<uint8_t> Bytes = *Val.getAsBlock();
if (DWARFAttribute::mayHaveLocationDescription(AttrSpec.Attr) &&
(Val.isFormClass(DWARFFormValue::FC_Block) ||
Val.isFormClass(DWARFFormValue::FC_Exprloc))) {
DWARFUnit &OrigUnit = Unit.getOrigUnit();
DataExtractor Data(StringRef((const char *), Bytes.size()),
IsLittleEndian, OrigUnit.getAddressByteSize());
DWARFExpression Expr(Data, OrigUnit.getVersion(),
cloneExpression(Data, Expr, DMO, Unit, Buffer);
Bytes = Buffer;
for (auto Byte : Bytes)
Attr->addValue(DIEAlloc, static_cast<dwarf::Attribute>(0),
dwarf::DW_FORM_data1, DIEInteger(Byte));
// FIXME: If DIEBlock and DIELoc just reuses the Size field of
// the DIE class, this if could be replaced by
// Attr->setSize(Bytes.size()).
if (Linker.Streamer) {
auto *AsmPrinter = &Linker.Streamer->getAsmPrinter();
if (Loc)
Die.addValue(DIEAlloc, Value);
return AttrSize;
unsigned DwarfLinker::DIECloner::cloneAddressAttribute(
DIE &Die, AttributeSpec AttrSpec, const DWARFFormValue &Val,
const CompileUnit &Unit, AttributesInfo &Info) {
uint64_t Addr = *Val.getAsAddress();
if (LLVM_UNLIKELY(Linker.Options.Update)) {
if (AttrSpec.Attr == dwarf::DW_AT_low_pc)
Info.HasLowPc = true;
Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
dwarf::Form(AttrSpec.Form), DIEInteger(Addr));
return Unit.getOrigUnit().getAddressByteSize();
if (AttrSpec.Attr == dwarf::DW_AT_low_pc) {
if (Die.getTag() == dwarf::DW_TAG_inlined_subroutine ||
Die.getTag() == dwarf::DW_TAG_lexical_block)
// The low_pc of a block or inline subroutine might get
// relocated because it happens to match the low_pc of the
// enclosing subprogram. To prevent issues with that, always use
// the low_pc from the input DIE if relocations have been applied.
Addr = (Info.OrigLowPc != std::numeric_limits<uint64_t>::max()
? Info.OrigLowPc
: Addr) +
else if (Die.getTag() == dwarf::DW_TAG_compile_unit) {
Addr = Unit.getLowPc();
if (Addr == std::numeric_limits<uint64_t>::max())
return 0;
Info.HasLowPc = true;
} else if (AttrSpec.Attr == dwarf::DW_AT_high_pc) {
if (Die.getTag() == dwarf::DW_TAG_compile_unit) {
if (uint64_t HighPc = Unit.getHighPc())
Addr = HighPc;
return 0;
} else
// If we have a high_pc recorded for the input DIE, use
// it. Otherwise (when no relocations where applied) just use the
// one we just decoded.
Addr = (Info.OrigHighPc ? Info.OrigHighPc : Addr) + Info.PCOffset;
Die.addValue(DIEAlloc, static_cast<dwarf::Attribute>(AttrSpec.Attr),
static_cast<dwarf::Form>(AttrSpec.Form), DIEInteger(Addr));
return Unit.getOrigUnit().getAddressByteSize();
unsigned DwarfLinker::DIECloner::cloneScalarAttribute(
DIE &Die, const DWARFDie &InputDIE, const DebugMapObject &DMO,
CompileUnit &Unit, AttributeSpec AttrSpec, const DWARFFormValue &Val,
unsigned AttrSize, AttributesInfo &Info) {
uint64_t Value;
if (LLVM_UNLIKELY(Linker.Options.Update)) {
if (auto OptionalValue = Val.getAsUnsignedConstant())
Value = *OptionalValue;
else if (auto OptionalValue = Val.getAsSignedConstant())
Value = *OptionalValue;
else if (auto OptionalValue = Val.getAsSectionOffset())
Value = *OptionalValue;
else {
"Unsupported scalar attribute form. Dropping attribute.", DMO,
return 0;
if (AttrSpec.Attr == dwarf::DW_AT_declaration && Value)
Info.IsDeclaration = true;
Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
dwarf::Form(AttrSpec.Form), DIEInteger(Value));
return AttrSize;
if (AttrSpec.Attr == dwarf::DW_AT_high_pc &&
Die.getTag() == dwarf::DW_TAG_compile_unit) {
if (Unit.getLowPc() == -1ULL)
return 0;
// Dwarf >= 4 high_pc is an size, not an address.
Value = Unit.getHighPc() - Unit.getLowPc();
} else if (AttrSpec.Form == dwarf::DW_FORM_sec_offset)
Value = *Val.getAsSectionOffset();
else if (AttrSpec.Form == dwarf::DW_FORM_sdata)
Value = *Val.getAsSignedConstant();
else if (auto OptionalValue = Val.getAsUnsignedConstant())
Value = *OptionalValue;
else {
"Unsupported scalar attribute form. Dropping attribute.", DMO,
return 0;
PatchLocation Patch =
Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
dwarf::Form(AttrSpec.Form), DIEInteger(Value));
if (AttrSpec.Attr == dwarf::DW_AT_ranges) {
Unit.noteRangeAttribute(Die, Patch);
Info.HasRanges = true;
// A more generic way to check for location attributes would be
// nice, but it's very unlikely that any other attribute needs a
// location list.
// FIXME: use DWARFAttribute::mayHaveLocationDescription().
else if (AttrSpec.Attr == dwarf::DW_AT_location ||
AttrSpec.Attr == dwarf::DW_AT_frame_base)
Unit.noteLocationAttribute(Patch, Info.PCOffset);
else if (AttrSpec.Attr == dwarf::DW_AT_declaration && Value)
Info.IsDeclaration = true;
return AttrSize;
/// Clone \p InputDIE's attribute described by \p AttrSpec with
/// value \p Val, and add it to \p Die.
/// \returns the size of the cloned attribute.
unsigned DwarfLinker::DIECloner::cloneAttribute(
DIE &Die, const DWARFDie &InputDIE, const DebugMapObject &DMO,
CompileUnit &Unit, OffsetsStringPool &StringPool, const DWARFFormValue &Val,
const AttributeSpec AttrSpec, unsigned AttrSize, AttributesInfo &Info,
bool IsLittleEndian) {
const DWARFUnit &U = Unit.getOrigUnit();
switch (AttrSpec.Form) {
case dwarf::DW_FORM_strp:
case dwarf::DW_FORM_string:
return cloneStringAttribute(Die, AttrSpec, Val, U, StringPool, Info);
case dwarf::DW_FORM_ref_addr:
case dwarf::DW_FORM_ref1:
case dwarf::DW_FORM_ref2:
case dwarf::DW_FORM_ref4:
case dwarf::DW_FORM_ref8:
return cloneDieReferenceAttribute(Die, InputDIE, AttrSpec, AttrSize, Val,
DMO, Unit);
case dwarf::DW_FORM_block:
case dwarf::DW_FORM_block1:
case dwarf::DW_FORM_block2:
case dwarf::DW_FORM_block4:
case dwarf::DW_FORM_exprloc:
return cloneBlockAttribute(Die, DMO, Unit, AttrSpec, Val, AttrSize,
case dwarf::DW_FORM_addr:
return cloneAddressAttribute(Die, AttrSpec, Val, Unit, Info);
case dwarf::DW_FORM_data1:
case dwarf::DW_FORM_data2:
case dwarf::DW_FORM_data4:
case dwarf::DW_FORM_data8:
case dwarf::DW_FORM_udata:
case dwarf::DW_FORM_sdata:
case dwarf::DW_FORM_sec_offset:
case dwarf::DW_FORM_flag:
case dwarf::DW_FORM_flag_present:
return cloneScalarAttribute(Die, InputDIE, DMO, Unit, AttrSpec, Val,
AttrSize, Info);
"Unsupported attribute form in cloneAttribute. Dropping.", DMO,
return 0;
/// Apply the valid relocations found by findValidRelocs() to
/// the buffer \p Data, taking into account that Data is at \p BaseOffset
/// in the debug_info section.
/// Like for findValidRelocs(), this function must be called with
/// monotonic \p BaseOffset values.
/// \returns whether any reloc has been applied.
bool DwarfLinker::RelocationManager::applyValidRelocs(
MutableArrayRef<char> Data, uint64_t BaseOffset, bool IsLittleEndian) {
assert((NextValidReloc == 0 ||
BaseOffset > ValidRelocs[NextValidReloc - 1].Offset) &&
"BaseOffset should only be increasing.");
if (NextValidReloc >= ValidRelocs.size())
return false;
// Skip relocs that haven't been applied.
while (NextValidReloc < ValidRelocs.size() &&
ValidRelocs[NextValidReloc].Offset < BaseOffset)
bool Applied = false;
uint64_t EndOffset = BaseOffset + Data.size();
while (NextValidReloc < ValidRelocs.size() &&
ValidRelocs[NextValidReloc].Offset >= BaseOffset &&
ValidRelocs[NextValidReloc].Offset < EndOffset) {
const auto &ValidReloc = ValidRelocs[NextValidReloc++];
assert(ValidReloc.Offset - BaseOffset < Data.size());
assert(ValidReloc.Offset - BaseOffset + ValidReloc.Size <= Data.size());
char Buf[8];
uint64_t Value = ValidReloc.Mapping->getValue().BinaryAddress;
Value += ValidReloc.Addend;
for (unsigned i = 0; i != ValidReloc.Size; ++i) {
unsigned Index = IsLittleEndian ? i : (ValidReloc.Size - i - 1);
Buf[i] = uint8_t(Value >> (Index * 8));
assert(ValidReloc.Size <= sizeof(Buf));
memcpy(&Data[ValidReloc.Offset - BaseOffset], Buf, ValidReloc.Size);
Applied = true;
return Applied;
static bool isObjCSelector(StringRef Name) {
return Name.size() > 2 && (Name[0] == '-' || Name[0] == '+') &&
(Name[1] == '[');
void DwarfLinker::DIECloner::addObjCAccelerator(CompileUnit &Unit,
const DIE *Die,
DwarfStringPoolEntryRef Name,
OffsetsStringPool &StringPool,
bool SkipPubSection) {
assert(isObjCSelector(Name.getString()) && "not an objc selector");
// Objective C method or class function.
// "- [Class(Category) selector :withArg ...]"
StringRef ClassNameStart(Name.getString().drop_front(2));
size_t FirstSpace = ClassNameStart.find(' ');
if (FirstSpace == StringRef::npos)
StringRef SelectorStart( + FirstSpace + 1);
if (!SelectorStart.size())
StringRef Selector(, SelectorStart.size() - 1);
Unit.addNameAccelerator(Die, StringPool.getEntry(Selector), SkipPubSection);
// Add an entry for the class name that points to this
// method/class function.
StringRef ClassName(, FirstSpace);
Unit.addObjCAccelerator(Die, StringPool.getEntry(ClassName), SkipPubSection);
if (ClassName[ClassName.size() - 1] == ')') {
size_t OpenParens = ClassName.find('(');
if (OpenParens != StringRef::npos) {
StringRef ClassNameNoCategory(, OpenParens);
Unit.addObjCAccelerator(Die, StringPool.getEntry(ClassNameNoCategory),
std::string MethodNameNoCategory(Name.getString().data(), OpenParens + 2);
// FIXME: The missing space here may be a bug, but
// dsymutil-classic also does it this way.
Unit.addNameAccelerator(Die, StringPool.getEntry(MethodNameNoCategory),
static bool
shouldSkipAttribute(DWARFAbbreviationDeclaration::AttributeSpec AttrSpec,
uint16_t Tag, bool InDebugMap, bool SkipPC,
bool InFunctionScope) {
switch (AttrSpec.Attr) {
return false;
case dwarf::DW_AT_low_pc:
case dwarf::DW_AT_high_pc:
case dwarf::DW_AT_ranges:
return SkipPC;
case dwarf::DW_AT_location:
case dwarf::DW_AT_frame_base:
// FIXME: for some reason dsymutil-classic keeps the location attributes
// when they are of block type (i.e. not location lists). This is totally
// wrong for globals where we will keep a wrong address. It is mostly
// harmless for locals, but there is no point in keeping these anyway when
// the function wasn't linked.
return (SkipPC || (!InFunctionScope && Tag == dwarf::DW_TAG_variable &&
!InDebugMap)) &&
DIE *DwarfLinker::DIECloner::cloneDIE(
const DWARFDie &InputDIE, const DebugMapObject &DMO, CompileUnit &Unit,
OffsetsStringPool &StringPool, int64_t PCOffset, uint32_t OutOffset,
unsigned Flags, bool IsLittleEndian, DIE *Die) {
DWARFUnit &U = Unit.getOrigUnit();
unsigned Idx = U.getDIEIndex(InputDIE);
CompileUnit::DIEInfo &Info = Unit.getInfo(Idx);
// Should the DIE appear in the output?
if (!Unit.getInfo(Idx).Keep)
return nullptr;
uint64_t Offset = InputDIE.getOffset();
assert(!(Die && Info.Clone) && "Can't supply a DIE and a cloned DIE");
if (!Die) {
// The DIE might have been already created by a forward reference
// (see cloneDieReferenceAttribute()).
if (!Info.Clone)
Info.Clone = DIE::get(DIEAlloc, dwarf::Tag(InputDIE.getTag()));
Die = Info.Clone;
assert(Die->getTag() == InputDIE.getTag());
if ((Unit.hasODR() || Unit.isClangModule()) && !Info.Incomplete &&
Die->getTag() != dwarf::DW_TAG_namespace && Info.Ctxt &&
Info.Ctxt != Unit.getInfo(Info.ParentIdx).Ctxt &&
!Info.Ctxt->getCanonicalDIEOffset()) {
// We are about to emit a DIE that is the root of its own valid
// DeclContext tree. Make the current offset the canonical offset
// for this context.
Info.Ctxt->setCanonicalDIEOffset(OutOffset + Unit.getStartOffset());
// Extract and clone every attribute.
DWARFDataExtractor Data = U.getDebugInfoExtractor();
// Point to the next DIE (generally there is always at least a NULL
// entry after the current one). If this is a lone
// DW_TAG_compile_unit without any children, point to the next unit.
uint64_t NextOffset = (Idx + 1 < U.getNumDIEs())
? U.getDIEAtIndex(Idx + 1).getOffset()
: U.getNextUnitOffset();
AttributesInfo AttrInfo;
// We could copy the data only if we need to apply a relocation to it. After
// testing, it seems there is no performance downside to doing the copy
// unconditionally, and it makes the code simpler.
SmallString<40> DIECopy(Data.getData().substr(Offset, NextOffset - Offset));
Data =
DWARFDataExtractor(DIECopy, Data.isLittleEndian(), Data.getAddressSize());
// Modify the copy with relocated addresses.
if (RelocMgr.applyValidRelocs(DIECopy, Offset, Data.isLittleEndian())) {
// If we applied relocations, we store the value of high_pc that was
// potentially stored in the input DIE. If high_pc is an address
// (Dwarf version == 2), then it might have been relocated to a
// totally unrelated value (because the end address in the object
// file might be start address of another function which got moved
// independently by the linker). The computation of the actual
// high_pc value is done in cloneAddressAttribute().
AttrInfo.OrigHighPc =
dwarf::toAddress(InputDIE.find(dwarf::DW_AT_high_pc), 0);
// Also store the low_pc. It might get relocated in an
// inline_subprogram that happens at the beginning of its
// inlining function.
AttrInfo.OrigLowPc = dwarf::toAddress(InputDIE.find(dwarf::DW_AT_low_pc),
// Reset the Offset to 0 as we will be working on the local copy of
// the data.
Offset = 0;
const auto *Abbrev = InputDIE.getAbbreviationDeclarationPtr();
Offset += getULEB128Size(Abbrev->getCode());
// We are entering a subprogram. Get and propagate the PCOffset.
if (Die->getTag() == dwarf::DW_TAG_subprogram)
PCOffset = Info.AddrAdjust;
AttrInfo.PCOffset = PCOffset;
if (Abbrev->getTag() == dwarf::DW_TAG_subprogram) {
Flags |= TF_InFunctionScope;
if (!Info.InDebugMap && LLVM_LIKELY(!Options.Update))
Flags |= TF_SkipPC;
bool Copied = false;
for (const auto &AttrSpec : Abbrev->attributes()) {
if (LLVM_LIKELY(!Options.Update) &&
shouldSkipAttribute(AttrSpec, Die->getTag(), Info.InDebugMap,
Flags & TF_SkipPC, Flags & TF_InFunctionScope)) {
DWARFFormValue::skipValue(AttrSpec.Form, Data, &Offset,
// FIXME: dsymutil-classic keeps the old abbreviation around
// even if it's not used. We can remove this (and the copyAbbrev
// helper) as soon as bit-for-bit compatibility is not a goal anymore.
if (!Copied) {
copyAbbrev(*InputDIE.getAbbreviationDeclarationPtr(), Unit.hasODR());
Copied = true;
DWARFFormValue Val(AttrSpec.Form);
uint64_t AttrSize = Offset;
Val.extractValue(Data, &Offset, U.getFormParams(), &U);
AttrSize = Offset - AttrSize;
OutOffset += cloneAttribute(*Die, InputDIE, DMO, Unit, StringPool, Val,
AttrSpec, AttrSize, AttrInfo, IsLittleEndian);
// Look for accelerator entries.
uint16_t Tag = InputDIE.getTag();
// FIXME: This is slightly wrong. An inline_subroutine without a
// low_pc, but with AT_ranges might be interesting to get into the
// accelerator tables too. For now stick with dsymutil's behavior.
if ((Info.InDebugMap || AttrInfo.HasLowPc || AttrInfo.HasRanges) &&
Tag != dwarf::DW_TAG_compile_unit &&
getDIENames(InputDIE, AttrInfo, StringPool,
Tag != dwarf::DW_TAG_inlined_subroutine)) {
if (AttrInfo.MangledName && AttrInfo.MangledName != AttrInfo.Name)
Unit.addNameAccelerator(Die, AttrInfo.MangledName,
Tag == dwarf::DW_TAG_inlined_subroutine);
if (AttrInfo.Name) {
if (AttrInfo.NameWithoutTemplate)
Unit.addNameAccelerator(Die, AttrInfo.NameWithoutTemplate,
/* SkipPubSection */ true);
Unit.addNameAccelerator(Die, AttrInfo.Name,
Tag == dwarf::DW_TAG_inlined_subroutine);
if (AttrInfo.Name && isObjCSelector(AttrInfo.Name.getString()))
addObjCAccelerator(Unit, Die, AttrInfo.Name, StringPool,
/* SkipPubSection =*/true);
} else if (Tag == dwarf::DW_TAG_namespace) {
if (!AttrInfo.Name)
AttrInfo.Name = StringPool.getEntry("(anonymous namespace)");
Unit.addNamespaceAccelerator(Die, AttrInfo.Name);
} else if (isTypeTag(Tag) && !AttrInfo.IsDeclaration &&
getDIENames(InputDIE, AttrInfo, StringPool) && AttrInfo.Name &&
AttrInfo.Name.getString()[0]) {
uint32_t Hash = hashFullyQualifiedName(InputDIE, Unit, DMO);
uint64_t RuntimeLang =
bool ObjCClassIsImplementation =
(RuntimeLang == dwarf::DW_LANG_ObjC ||
RuntimeLang == dwarf::DW_LANG_ObjC_plus_plus) &&
Unit.addTypeAccelerator(Die, AttrInfo.Name, ObjCClassIsImplementation,
// Determine whether there are any children that we want to keep.
bool HasChildren = false;
for (auto Child : InputDIE.children()) {
unsigned Idx = U.getDIEIndex(Child);
if (Unit.getInfo(Idx).Keep) {
HasChildren = true;
DIEAbbrev NewAbbrev = Die->generateAbbrev();
if (HasChildren)
// Assign a permanent abbrev number
// Add the size of the abbreviation number to the output offset.
OutOffset += getULEB128Size(Die->getAbbrevNumber());
if (!HasChildren) {
// Update our size.
Die->setSize(OutOffset - Die->getOffset());
return Die;
// Recursively clone children.
for (auto Child : InputDIE.children()) {
if (DIE *Clone = cloneDIE(Child, DMO, Unit, StringPool, PCOffset, OutOffset,
Flags, IsLittleEndian)) {
OutOffset = Clone->getOffset() + Clone->getSize();
// Account for the end of children marker.
OutOffset += sizeof(int8_t);
// Update our size.
Die->setSize(OutOffset - Die->getOffset());
return Die;
/// Patch the input object file relevant debug_ranges entries
/// and emit them in the output file. Update the relevant attributes
/// to point at the new entries.
void DwarfLinker::patchRangesForUnit(const CompileUnit &Unit,
DWARFContext &OrigDwarf,
const DebugMapObject &DMO) const {
DWARFDebugRangeList RangeList;
const auto &FunctionRanges = Unit.getFunctionRanges();
unsigned AddressSize = Unit.getOrigUnit().getAddressByteSize();
DWARFDataExtractor RangeExtractor(OrigDwarf.getDWARFObj(),
OrigDwarf.isLittleEndian(), AddressSize);
auto InvalidRange = FunctionRanges.end(), CurrRange = InvalidRange;
DWARFUnit &OrigUnit = Unit.getOrigUnit();
auto OrigUnitDie = OrigUnit.getUnitDIE(false);
uint64_t OrigLowPc =
dwarf::toAddress(OrigUnitDie.find(dwarf::DW_AT_low_pc), -1ULL);
// Ranges addresses are based on the unit's low_pc. Compute the
// offset we need to apply to adapt to the new unit's low_pc.
int64_t UnitPcOffset = 0;
if (OrigLowPc != -1ULL)
UnitPcOffset = int64_t(OrigLowPc) - Unit.getLowPc();
for (const auto &RangeAttribute : Unit.getRangesAttributes()) {
uint64_t Offset = RangeAttribute.get();
if (Error E = RangeList.extract(RangeExtractor, &Offset)) {
reportWarning("invalid range list ignored.", DMO);
const auto &Entries = RangeList.getEntries();
if (!Entries.empty()) {
const DWARFDebugRangeList::RangeListEntry &First = Entries.front();
if (CurrRange == InvalidRange ||
First.StartAddress + OrigLowPc < CurrRange.start() ||
First.StartAddress + OrigLowPc >= CurrRange.stop()) {
CurrRange = FunctionRanges.find(First.StartAddress + OrigLowPc);
if (CurrRange == InvalidRange ||
CurrRange.start() > First.StartAddress + OrigLowPc) {
reportWarning("no mapping for range.", DMO);
Streamer->emitRangesEntries(UnitPcOffset, OrigLowPc, CurrRange, Entries,
/// Generate the debug_aranges entries for \p Unit and if the
/// unit has a DW_AT_ranges attribute, also emit the debug_ranges
/// contribution for this attribute.
/// FIXME: this could actually be done right in patchRangesForUnit,
/// but for the sake of initial bit-for-bit compatibility with legacy
/// dsymutil, we have to do it in a delayed pass.
void DwarfLinker::generateUnitRanges(CompileUnit &Unit) const {
auto Attr = Unit.getUnitRangesAttribute();
if (Attr)
Streamer->emitUnitRangesEntries(Unit, static_cast<bool>(Attr));
/// Insert the new line info sequence \p Seq into the current
/// set of already linked line info \p Rows.
static void insertLineSequence(std::vector<DWARFDebugLine::Row> &Seq,
std::vector<DWARFDebugLine::Row> &Rows) {
if (Seq.empty())
if (!Rows.empty() && Rows.back().Address < Seq.front().Address) {
Rows.insert(Rows.end(), Seq.begin(), Seq.end());
object::SectionedAddress Front = Seq.front().Address;
auto InsertPoint = partition_point(
Rows, [=](const DWARFDebugLine::Row &O) { return O.Address < Front; });
// FIXME: this only removes the unneeded end_sequence if the
// sequences have been inserted in order. Using a global sort like
// described in patchLineTableForUnit() and delaying the end_sequene
// elimination to emitLineTableForUnit() we can get rid of all of them.
if (InsertPoint != Rows.end() && InsertPoint->Address == Front &&
InsertPoint->EndSequence) {
*InsertPoint = Seq.front();
Rows.insert(InsertPoint + 1, Seq.begin() + 1, Seq.end());
} else {
Rows.insert(InsertPoint, Seq.begin(), Seq.end());
static void patchStmtList(DIE &Die, DIEInteger Offset) {
for (auto &V : Die.values())
if (V.getAttribute() == dwarf::DW_AT_stmt_list) {
V = DIEValue(V.getAttribute(), V.getForm(), Offset);
llvm_unreachable("Didn't find DW_AT_stmt_list in cloned DIE!");
/// Extract the line table for \p Unit from \p OrigDwarf, and
/// recreate a relocated version of these for the address ranges that
/// are present in the binary.
void DwarfLinker::patchLineTableForUnit(CompileUnit &Unit,
DWARFContext &OrigDwarf,
RangesTy &Ranges,
const DebugMapObject &DMO) {
DWARFDie CUDie = Unit.getOrigUnit().getUnitDIE();
auto StmtList = dwarf::toSectionOffset(CUDie.find(dwarf::DW_AT_stmt_list));
if (!StmtList)
// Update the cloned DW_AT_stmt_list with the correct debug_line offset.
if (auto *OutputDIE = Unit.getOutputUnitDIE())
patchStmtList(*OutputDIE, DIEInteger(Streamer->getLineSectionSize()));
// Parse the original line info for the unit.
DWARFDebugLine::LineTable LineTable;
uint64_t StmtOffset = *StmtList;
DWARFDataExtractor LineExtractor(
OrigDwarf.getDWARFObj(), OrigDwarf.getDWARFObj().getLineSection(),
OrigDwarf.isLittleEndian(), Unit.getOrigUnit().getAddressByteSize());
if (Options.Translator)
return Streamer->translateLineTable(LineExtractor, StmtOffset);
Error Err = LineTable.parse(LineExtractor, &StmtOffset, OrigDwarf,
&Unit.getOrigUnit(), DWARFContext::dumpWarning);
// This vector is the output line table.
std::vector<DWARFDebugLine::Row> NewRows;
// Current sequence of rows being extracted, before being inserted
// in NewRows.
std::vector<DWARFDebugLine::Row> Seq;
const auto &FunctionRanges = Unit.getFunctionRanges();
auto InvalidRange = FunctionRanges.end(), CurrRange = InvalidRange;
// FIXME: This logic is meant to generate exactly the same output as
// Darwin's classic dsymutil. There is a nicer way to implement this
// by simply putting all the relocated line info in NewRows and simply
// sorting NewRows before passing it to emitLineTableForUnit. This
// should be correct as sequences for a function should stay
// together in the sorted output. There are a few corner cases that
// look suspicious though, and that required to implement the logic
// this way. Revisit that once initial validation is finished.
// Iterate over the object file line info and extract the sequences
// that correspond to linked functions.
for (auto &Row : LineTable.Rows) {
// Check whether we stepped out of the range. The range is
// half-open, but consider accept the end address of the range if
// it is marked as end_sequence in the input (because in that
// case, the relocation offset is accurate and that entry won't
// serve as the start of another function).
if (CurrRange == InvalidRange || Row.Address.Address < CurrRange.start() ||
Row.Address.Address > CurrRange.stop() ||
(Row.Address.Address == CurrRange.stop() && !Row.EndSequence)) {
// We just stepped out of a known range. Insert a end_sequence
// corresponding to the end of the range.
uint64_t StopAddress = CurrRange != InvalidRange
? CurrRange.stop() + CurrRange.value()
: -1ULL;
CurrRange = FunctionRanges.find(Row.Address.Address);
bool CurrRangeValid =
CurrRange != InvalidRange && CurrRange.start() <= Row.Address.Address;
if (!CurrRangeValid) {
CurrRange = InvalidRange;
if (StopAddress != -1ULL) {
// Try harder by looking in the DebugMapObject function
// ranges map. There are corner cases where this finds a
// valid entry. It's unclear if this is right or wrong, but
// for now do as dsymutil.
// FIXME: Understand exactly what cases this addresses and
// potentially remove it along with the Ranges map.
auto Range = Ranges.lower_bound(Row.Address.Address);
if (Range != Ranges.begin() && Range != Ranges.end())
if (Range != Ranges.end() && Range->first <= Row.Address.Address &&
Range->second.HighPC >= Row.Address.Address) {
StopAddress = Row.Address.Address + Range->second.Offset;
if (StopAddress != -1ULL && !Seq.empty()) {
// Insert end sequence row with the computed end address, but
// the same line as the previous one.
auto NextLine = Seq.back();
NextLine.Address.Address = StopAddress;
NextLine.EndSequence = 1;
NextLine.PrologueEnd = 0;
NextLine.BasicBlock = 0;
NextLine.EpilogueBegin = 0;
insertLineSequence(Seq, NewRows);
if (!CurrRangeValid)
// Ignore empty sequences.
if (Row.EndSequence && Seq.empty())
// Relocate row address and add it to the current sequence.
Row.Address.Address += CurrRange.value();
if (Row.EndSequence)
insertLineSequence(Seq, NewRows);
// Finished extracting, now emit the line tables.
// FIXME: LLVM hard-codes its prologue values. We just copy the
// prologue over and that works because we act as both producer and
// consumer. It would be nicer to have a real configurable line
// table emitter.
if (LineTable.Prologue.getVersion() < 2 ||
LineTable.Prologue.getVersion() > 5 ||
LineTable.Prologue.DefaultIsStmt != DWARF2_LINE_DEFAULT_IS_STMT ||
LineTable.Prologue.OpcodeBase > 13)
reportWarning("line table parameters mismatch. Cannot emit.", DMO);
else {
uint32_t PrologueEnd = *StmtList + 10 + LineTable.Prologue.PrologueLength;
// DWARF v5 has an extra 2 bytes of information before the header_length
// field.
if (LineTable.Prologue.getVersion() == 5)
PrologueEnd += 2;
StringRef LineData = OrigDwarf.getDWARFObj().getLineSection().Data;
MCDwarfLineTableParams Params;
Params.DWARF2LineOpcodeBase = LineTable.Prologue.OpcodeBase;
Params.DWARF2LineBase = LineTable.Prologue.LineBase;
Params.DWARF2LineRange = LineTable.Prologue.LineRange;
LineData.slice(*StmtList + 4, PrologueEnd),
LineTable.Prologue.MinInstLength, NewRows,
void DwarfLinker::emitAcceleratorEntriesForUnit(CompileUnit &Unit) {
switch (Options.TheAccelTableKind) {
case AccelTableKind::Apple:
case AccelTableKind::Dwarf:
case AccelTableKind::Default:
llvm_unreachable("The default must be updated to a concrete value.");
void DwarfLinker::emitAppleAcceleratorEntriesForUnit(CompileUnit &Unit) {
// Add namespaces.
for (const auto &Namespace : Unit.getNamespaces())
Namespace.Die->getOffset() + Unit.getStartOffset());
/// Add names.
if (!Options.Minimize)
for (const auto &Pubname : Unit.getPubnames())
Pubname.Die->getOffset() + Unit.getStartOffset());
/// Add types.
if (!Options.Minimize)
for (const auto &Pubtype : Unit.getPubtypes())
Pubtype.Name, Pubtype.Die->getOffset() + Unit.getStartOffset(),
Pubtype.ObjcClassImplementation ? dwarf::DW_FLAG_type_implementation
: 0,
/// Add ObjC names.
for (const auto &ObjC : Unit.getObjC())
AppleObjc.addName(ObjC.Name, ObjC.Die->getOffset() + Unit.getStartOffset());
void DwarfLinker::emitDwarfAcceleratorEntriesForUnit(CompileUnit &Unit) {
for (const auto &Namespace : Unit.getNamespaces())
DebugNames.addName(Namespace.Name, Namespace.Die->getOffset(),
Namespace.Die->getTag(), Unit.getUniqueID());
for (const auto &Pubname : Unit.getPubnames())
DebugNames.addName(Pubname.Name, Pubname.Die->getOffset(),
Pubname.Die->getTag(), Unit.getUniqueID());
for (const auto &Pubtype : Unit.getPubtypes())
DebugNames.addName(Pubtype.Name, Pubtype.Die->getOffset(),
Pubtype.Die->getTag(), Unit.getUniqueID());
/// Read the frame info stored in the object, and emit the
/// patched frame descriptions for the linked binary.
/// This is actually pretty easy as the data of the CIEs and FDEs can
/// be considered as black boxes and moved as is. The only thing to do
/// is to patch the addresses in the headers.
void DwarfLinker::patchFrameInfoForObject(const DebugMapObject &DMO,
RangesTy &Ranges,
DWARFContext &OrigDwarf,
unsigned AddrSize) {
StringRef FrameData = OrigDwarf.getDWARFObj().getFrameSection().Data;
if (FrameData.empty())
DataExtractor Data(FrameData, OrigDwarf.isLittleEndian(), 0);
uint64_t InputOffset = 0;
// Store the data of the CIEs defined in this object, keyed by their
// offsets.
DenseMap<uint64_t, StringRef> LocalCIES;
while (Data.isValidOffset(InputOffset)) {
uint64_t EntryOffset = InputOffset;
uint32_t InitialLength = Data.getU32(&InputOffset);
if (InitialLength == 0xFFFFFFFF)
return reportWarning("Dwarf64 bits no supported", DMO);
uint32_t CIEId = Data.getU32(&InputOffset);
if (CIEId == 0xFFFFFFFF) {
// This is a CIE, store it.
StringRef CIEData = FrameData.substr(EntryOffset, InitialLength + 4);
LocalCIES[EntryOffset] = CIEData;
// The -4 is to account for the CIEId we just read.
InputOffset += InitialLength - 4;
uint32_t Loc = Data.getUnsigned(&InputOffset, AddrSize);
// Some compilers seem to emit frame info that doesn't start at
// the function entry point, thus we can't just lookup the address
// in the debug map. Use the linker's range map to see if the FDE
// describes something that we can relocate.
auto Range = Ranges.upper_bound(Loc);
if (Range != Ranges.begin())
if (Range == Ranges.end() || Range->first > Loc ||
Range->second.HighPC <= Loc) {
// The +4 is to account for the size of the InitialLength field itself.
InputOffset = EntryOffset + InitialLength + 4;
// This is an FDE, and we have a mapping.
// Have we already emitted a corresponding CIE?
StringRef CIEData = LocalCIES[CIEId];
if (CIEData.empty())
return reportWarning("Inconsistent debug_frame content. Dropping.", DMO);
// Look if we already emitted a CIE that corresponds to the
// referenced one (the CIE data is the key of that lookup).
auto IteratorInserted = EmittedCIEs.insert(
std::make_pair(CIEData, Streamer->getFrameSectionSize()));
// If there is no CIE yet for this ID, emit it.
if (IteratorInserted.second ||
// FIXME: dsymutil-classic only caches the last used CIE for
// reuse. Mimic that behavior for now. Just removing that
// second half of the condition and the LastCIEOffset variable
// makes the code DTRT.
LastCIEOffset != IteratorInserted.first->getValue()) {
LastCIEOffset = Streamer->getFrameSectionSize();
IteratorInserted.first->getValue() = LastCIEOffset;
// Emit the FDE with updated address and CIE pointer.
// (4 + AddrSize) is the size of the CIEId + initial_location
// fields that will get reconstructed by emitFDE().
unsigned FDERemainingBytes = InitialLength - (4 + AddrSize);
Streamer->emitFDE(IteratorInserted.first->getValue(), AddrSize,
Loc + Range->second.Offset,
FrameData.substr(InputOffset, FDERemainingBytes));
InputOffset += FDERemainingBytes;
void DwarfLinker::DIECloner::copyAbbrev(
const DWARFAbbreviationDeclaration &Abbrev, bool hasODR) {
DIEAbbrev Copy(dwarf::Tag(Abbrev.getTag()),
for (const auto &Attr : Abbrev.attributes()) {
uint16_t Form = Attr.Form;
if (hasODR && isODRAttribute(Attr.Attr))
Form = dwarf::DW_FORM_ref_addr;
Copy.AddAttribute(dwarf::Attribute(Attr.Attr), dwarf::Form(Form));
DwarfLinker::DIECloner::hashFullyQualifiedName(DWARFDie DIE, CompileUnit &U,
const DebugMapObject &DMO,
int ChildRecurseDepth) {
const char *Name = nullptr;
DWARFUnit *OrigUnit = &U.getOrigUnit();
CompileUnit *CU = &U;
Optional<DWARFFormValue> Ref;
while (1) {
if (const char *CurrentName = DIE.getName(DINameKind::ShortName))
Name = CurrentName;
if (!(Ref = DIE.find(dwarf::DW_AT_specification)) &&
!(Ref = DIE.find(dwarf::DW_AT_abstract_origin)))
if (!Ref->isFormClass(DWARFFormValue::FC_Reference))
CompileUnit *RefCU;
if (auto RefDIE =
resolveDIEReference(Linker, DMO, CompileUnits, *Ref, DIE, RefCU)) {
CU = RefCU;
OrigUnit = &RefCU->getOrigUnit();
unsigned Idx = OrigUnit->getDIEIndex(DIE);
if (!Name && DIE.getTag() == dwarf::DW_TAG_namespace)
Name = "(anonymous namespace)";
if (CU->getInfo(Idx).ParentIdx == 0 ||
// FIXME: dsymutil-classic compatibility. Ignore modules.
CU->getOrigUnit().getDIEAtIndex(CU->getInfo(Idx).ParentIdx).getTag() ==
return djbHash(Name ? Name : "", djbHash(ChildRecurseDepth ? "" : "::"));
DWARFDie Die = OrigUnit->getDIEAtIndex(CU->getInfo(Idx).ParentIdx);
return djbHash(
(Name ? Name : ""),
djbHash((Name ? "::" : ""),
hashFullyQualifiedName(Die, *CU, DMO, ++ChildRecurseDepth)));
static uint64_t getDwoId(const DWARFDie &CUDie, const DWARFUnit &Unit) {
auto DwoId = dwarf::toUnsigned(
CUDie.find({dwarf::DW_AT_dwo_id, dwarf::DW_AT_GNU_dwo_id}));
if (DwoId)
return *DwoId;
return 0;
bool DwarfLinker::registerModuleReference(
DWARFDie CUDie, const DWARFUnit &Unit, DebugMap &ModuleMap,
const DebugMapObject &DMO, RangesTy &Ranges, OffsetsStringPool &StringPool,
UniquingStringPool &UniquingStringPool, DeclContextTree &ODRContexts,
uint64_t ModulesEndOffset, unsigned &UnitID, bool IsLittleEndian,
unsigned Indent, bool Quiet) {
std::string PCMfile = dwarf::toString(
CUDie.find({dwarf::DW_AT_dwo_name, dwarf::DW_AT_GNU_dwo_name}), "");
if (PCMfile.empty())
return false;
// Clang module DWARF skeleton CUs abuse this for the path to the module.
uint64_t DwoId = getDwoId(CUDie, Unit);
std::string Name = dwarf::toString(CUDie.find(dwarf::DW_AT_name), "");
if (Name.empty()) {
if (!Quiet)
reportWarning("Anonymous module skeleton CU for " + PCMfile, DMO);
return true;
if (!Quiet && Options.Verbose) {
outs() << "Found clang module reference " << PCMfile;
auto Cached = ClangModules.find(PCMfile);
if (Cached != ClangModules.end()) {
// FIXME: Until PR27449 ( is
// fixed in clang, only warn about DWO_id mismatches in verbose mode.
// ASTFileSignatures will change randomly when a module is rebuilt.
if (!Quiet && Options.Verbose && (Cached->second != DwoId))
reportWarning(Twine("hash mismatch: this object file was built against a "
"different version of the module ") +
if (!Quiet && Options.Verbose)
outs() << " [cached].\n";
return true;
if (!Quiet && Options.Verbose)
outs() << " ...\n";
// Cyclic dependencies are disallowed by Clang, but we still
// shouldn't run into an infinite loop, so mark it as processed now.
ClangModules.insert({PCMfile, DwoId});
if (Error E = loadClangModule(CUDie, PCMfile, Name, DwoId, ModuleMap, DMO,
Ranges, StringPool, UniquingStringPool,
ODRContexts, ModulesEndOffset, UnitID,
IsLittleEndian, Indent + 2, Quiet)) {
return false;
return true;
ErrorOr<const object::ObjectFile &>
DwarfLinker::loadObject(const DebugMapObject &Obj, const DebugMap &Map) {
auto ObjectEntry =
BinHolder.getObjectEntry(Obj.getObjectFilename(), Obj.getTimestamp());
if (!ObjectEntry) {
auto Err = ObjectEntry.takeError();
Twine(Obj.getObjectFilename()) + ": " + toString(std::move(Err)), Obj);
return errorToErrorCode(std::move(Err));
auto Object = ObjectEntry->getObject(Map.getTriple());
if (!Object) {
auto Err = Object.takeError();
Twine(Obj.getObjectFilename()) + ": " + toString(std::move(Err)), Obj);
return errorToErrorCode(std::move(Err));
return *Object;
Error DwarfLinker::loadClangModule(
DWARFDie CUDie, StringRef Filename, StringRef ModuleName, uint64_t DwoId,
DebugMap &ModuleMap, const DebugMapObject &DMO, RangesTy &Ranges,
OffsetsStringPool &StringPool, UniquingStringPool &UniquingStringPool,
DeclContextTree &ODRContexts, uint64_t ModulesEndOffset, unsigned &UnitID,
bool IsLittleEndian, unsigned Indent, bool Quiet) {
/// Using a SmallString<0> because loadClangModule() is recursive.
SmallString<0> Path(Options.PrependPath);
if (sys::path::is_relative(Filename))
resolveRelativeObjectPath(Path, CUDie);
sys::path::append(Path, Filename);
// Don't use the cached binary holder because we have no thread-safety
// guarantee and the lifetime is limited.
auto &Obj = ModuleMap.addDebugMapObject(
Path, sys::TimePoint<std::chrono::seconds>(), MachO::N_OSO);
auto ErrOrObj = loadObject(Obj, ModuleMap);
if (!ErrOrObj) {
// Try and emit more helpful warnings by applying some heuristics.
StringRef ObjFile = DMO.getObjectFilename();
bool isClangModule = sys::path::extension(Filename).equals(".pcm");
bool isArchive = ObjFile.endswith(")");
if (isClangModule) {
StringRef ModuleCacheDir = sys::path::parent_path(Path);
if (sys::fs::exists(ModuleCacheDir)) {
// If the module's parent directory exists, we assume that the module
// cache has expired and was pruned by clang. A more adventurous
// dsymutil would invoke clang to rebuild the module now.
if (!ModuleCacheHintDisplayed) {
WithColor::note() << "The clang module cache may have expired since "
"this object file was built. Rebuilding the "
"object file will rebuild the module cache.\n";
ModuleCacheHintDisplayed = true;
} else if (isArchive) {
// If the module cache directory doesn't exist at all and the object
// file is inside a static library, we assume that the static library
// was built on a different machine. We don't want to discourage module
// debugging for convenience libraries within a project though.
if (!ArchiveHintDisplayed) {
<< "Linking a static library that was built with "
"-gmodules, but the module cache was not found. "
"Redistributable static libraries should never be "
"built with module debugging enabled. The debug "
"experience will be degraded due to incomplete "
"debug information.\n";
ArchiveHintDisplayed = true;
return Error::success();
std::unique_ptr<CompileUnit> Unit;
// Setup access to the debug info.
auto DwarfContext = DWARFContext::create(*ErrOrObj);
RelocationManager RelocMgr(*this);
for (const auto &CU : DwarfContext->compile_units()) {
// Recursively get all modules imported by this one.
auto CUDie = CU->getUnitDIE(false);
if (!CUDie)
if (!registerModuleReference(CUDie, *CU, ModuleMap, DMO, Ranges, StringPool,
UniquingStringPool, ODRContexts,
ModulesEndOffset, UnitID, IsLittleEndian,
Indent, Quiet)) {
if (Unit) {
std::string Err =
(Filename +
": Clang modules are expected to have exactly 1 compile unit.\n")
return make_error<StringError>(Err, inconvertibleErrorCode());
// FIXME: Until PR27449 ( is
// fixed in clang, only warn about DWO_id mismatches in verbose mode.
// ASTFileSignatures will change randomly when a module is rebuilt.
uint64_t PCMDwoId = getDwoId(CUDie, *CU);
if (PCMDwoId != DwoId) {
if (!Quiet && Options.Verbose)
Twine("hash mismatch: this object file was built against a "
"different version of the module ") +
// Update the cache entry with the DwoId of the module loaded from disk.
ClangModules[Filename] = PCMDwoId;
// Add this module.
Unit = std::make_unique<CompileUnit>(*CU, UnitID++, !Options.NoODR,
analyzeContextInfo(CUDie, 0, *Unit, &ODRContexts.getRoot(),
UniquingStringPool, ODRContexts, ModulesEndOffset,
[&](const Twine &Warning, const DWARFDie &DIE) {
reportWarning(Warning, DMO, &DIE);
// Keep everything.
if (!Unit->getOrigUnit().getUnitDIE().hasChildren())
return Error::success();
if (!Quiet && Options.Verbose) {
outs() << "cloning .debug_info from " << Filename << "\n";
UnitListTy CompileUnits;
DIECloner(*this, RelocMgr, DIEAlloc, CompileUnits, Options)
.cloneAllCompileUnits(*DwarfContext, DMO, Ranges, StringPool,
return Error::success();