MC: Implement support for new .addrsig and .addrsig_sym directives.

[pcc]

Summary

Part of the address-significance tables proposal:
http://lists.llvm.org/pipermail/llvm-dev/2018-May/123514.html

[pcc]

• Add a dwo test

[pcc]

Ping.

[echristo]

LGTM. Thanks and sorry for the delay.

llvm/docs/Extensions.rst

 
 ``.cg_profile`` directives are processed at the end of the file.  It is an error
 if either ``from`` or ``to`` are undefined temporary symbols.  If either symbol
 is a temporary symbol, then the section symbol is used instead.  If either
 symbol is undefined, then that symbol is defined as if ``.weak symbol`` has been
 written at the end of the file.  This forces the symbol to show up in the symbol
 table.
 
+``SHT_LLVM_ADDRSIG`` Section (address-significance table)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This section is used to mark symbols as address-significant, i.e. the address
+of the symbol is used in a comparison or leaks outside the translation unit. It
+has the same meaning as the absence of the LLVM attributes ``unnamed_addr``
+and ``local_unnamed_addr``.
+
+Any sections referred to by symbols that are not marked as address-significant
+in any object file may be safely merged by a linker without breaking the
+address uniqueness guarantee provided by the C and C++ language standards.
+
+The contents of the section are a sequence of ULEB128-encoded integers
+referring to the symbol table indexes of the address-significant symbols.
+
+There are two associated assembly directives:
+
+.. code-block:: gas
+
+  .addrsig
+
+This instructs the assembler to emit an address-significance table. Without
+this directive, all symbols are considered address-significant.
+
+.. code-block:: gas
+
+  .addrsig_sym sym
+
+This marks ``sym`` as address-significant.
+
 Target Specific Behaviour
 =========================
 
 X86
 ---
 
 Relocations
 ^^^^^^^^^^^

llvm/include/llvm/BinaryFormat/ELF.h

enum : unsigned {
   SHT_LOOS = 0x60000000,                // Lowest operating system-specific type.
   // Android packed relocation section types.
   // https://android.googlesource.com/platform/bionic/+/6f12bfece5dcc01325e0abba56a46b1bcf991c69/tools/relocation_packer/src/elf_file.cc#37
   SHT_ANDROID_REL = 0x60000001,
   SHT_ANDROID_RELA = 0x60000002,
   SHT_LLVM_ODRTAB = 0x6fff4c00,         // LLVM ODR table.
   SHT_LLVM_LINKER_OPTIONS = 0x6fff4c01, // LLVM Linker Options.
   SHT_LLVM_CALL_GRAPH_PROFILE = 0x6fff4c02, // LLVM Call Graph Profile.
+  SHT_LLVM_ADDRSIG = 0x6fff4c03,        // List of address-significant symbols
+                                        // for safe ICF.
   SHT_GNU_ATTRIBUTES = 0x6ffffff5,      // Object attributes.
   SHT_GNU_HASH = 0x6ffffff6,            // GNU-style hash table.
   SHT_GNU_verdef = 0x6ffffffd,          // GNU version definitions.
   SHT_GNU_verneed = 0x6ffffffe,         // GNU version references.
   SHT_GNU_versym = 0x6fffffff,          // GNU symbol versions table.
   SHT_HIOS = 0x6fffffff,                // Highest operating system-specific type.
   SHT_LOPROC = 0x70000000,              // Lowest processor arch-specific type.
   // Fixme: All this is duplicated in MCSectionELF. Why??

llvm/include/llvm/MC/MCObjectStreamer.h

bool EmitRelocDirective(const MCExpr &Offset, StringRef Name,
                           const MCExpr *Expr, SMLoc Loc) override;
   using MCStreamer::emitFill;
   void emitFill(const MCExpr &NumBytes, uint64_t FillValue,
                 SMLoc Loc = SMLoc()) override;
   void emitFill(const MCExpr &NumValues, int64_t Size, int64_t Expr,
                 SMLoc Loc = SMLoc()) override;
   void EmitFileDirective(StringRef Filename) override;
 
+  void EmitAddrsig() override;
+  void EmitAddrsigSym(const MCSymbol *Sym) override;
+
   void FinishImpl() override;
 
   /// Emit the absolute difference between two symbols if possible.
   ///
   /// Emit the absolute difference between \c Hi and \c Lo, as long as we can
   /// compute it.  Currently, that requires that both symbols are in the same
   /// data fragment.  Otherwise, do nothing and return \c false.
   ///

llvm/include/llvm/MC/MCObjectWriter.h

virtual bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
                                                       bool InSet) const;
 
   virtual bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
                                                       const MCSymbol &SymA,
                                                       const MCFragment &FB,
                                                       bool InSet,
                                                       bool IsPCRel) const;
 
+  /// Tell the object writer to emit an address-significance table during
+  /// writeObject(). If this function is not called, all symbols are treated as
+  /// address-significant.
+  virtual void emitAddrsigSection() {}
+
+  /// Record the given symbol in the address-significance table to be written
+  /// diring writeObject().
+  virtual void addAddrsigSymbol(const MCSymbol *Sym) {}
+
   /// Write the object file and returns the number of bytes written.
   ///
   /// This routine is called by the assembler after layout and relaxation is
   /// complete, fixups have been evaluated and applied, and relocations
   /// generated.
   virtual uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) = 0;
 
   /// @}

llvm/include/llvm/MC/MCStreamer.h

public:
   /// Emit a .reloc directive.
   /// Returns true if the relocation could not be emitted because Name is not
   /// known.
   virtual bool EmitRelocDirective(const MCExpr &Offset, StringRef Name,
                                   const MCExpr *Expr, SMLoc Loc) {
     return true;
   }
 
+  virtual void EmitAddrsig() {}
+  virtual void EmitAddrsigSym(const MCSymbol *Sym) {}
+
   /// Emit the given \p Instruction into the current section.
   /// PrintSchedInfo == true then schedul comment should be added to output
   virtual void EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
                                bool PrintSchedInfo = false);
 
   /// Set the bundle alignment mode from now on in the section.
   /// The argument is the power of 2 to which the alignment is set. The
   /// value 0 means turn the bundle alignment off.

llvm/lib/MC/ELFObjectWriter.cpp

 #include "llvm/MC/StringTableBuilder.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Host.h"
+#include "llvm/Support/LEB128.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/StringSaver.h"
 #include "llvm/Support/SwapByteOrder.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
public:
   /// \param Asm - The assembler.
   /// \param SectionIndexMap - Maps a section to its index.
   /// \param RevGroupMap - Maps a signature symbol to the group section.
   void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
                           const SectionIndexMapTy &SectionIndexMap,
                           const RevGroupMapTy &RevGroupMap,
                           SectionOffsetsTy &SectionOffsets);
 
+  void writeAddrsigSection();
+
   MCSectionELF *createRelocationSection(MCContext &Ctx,
                                         const MCSectionELF &Sec);
 
   const MCSectionELF *createStringTable(MCContext &Ctx);
 
   void writeSectionHeader(const MCAsmLayout &Layout,
                           const SectionIndexMapTy &SectionIndexMap,
                           const SectionOffsetsTy &SectionOffsets);

 class ELFObjectWriter : public MCObjectWriter {
   /// The target specific ELF writer instance.
   std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
 
   DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>> Relocations;
 
   DenseMap<const MCSymbolELF *, const MCSymbolELF *> Renames;
 
+  bool EmitAddrsigSection = false;
+  std::vector<const MCSymbol *> AddrsigSyms;
+
   bool hasRelocationAddend() const;
 
   bool shouldRelocateWithSymbol(const MCAssembler &Asm,
                                 const MCSymbolRefExpr *RefA,
                                 const MCSymbolELF *Sym, uint64_t C,
                                 unsigned Type) const;
 
 public:
public:
 
   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
                         const MCFragment *Fragment, const MCFixup &Fixup,
                         MCValue Target, uint64_t &FixedValue) override;
 
   void executePostLayoutBinding(MCAssembler &Asm,
                                 const MCAsmLayout &Layout) override;
 
+  void emitAddrsigSection() override { EmitAddrsigSection = true; }
+  void addAddrsigSymbol(const MCSymbol *Sym) override {
+    AddrsigSyms.push_back(Sym);
+  }
+
   friend struct ELFWriter;
 };
 
 class ELFSingleObjectWriter : public ELFObjectWriter {
   raw_pwrite_stream &OS;
   bool IsLittleEndian;
 
 public:
void ELFWriter::computeSymbolTable(
   const MCSectionELF *SymtabShndxSection =
       SectionTable[SymtabShndxSectionIndex - 1];
   for (uint32_t Index : ShndxIndexes)
     write(Index);
   SecEnd = W.OS.tell();
   SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
 }
 
+void ELFWriter::writeAddrsigSection() {
+  for (const MCSymbol *Sym : OWriter.AddrsigSyms)
+    encodeULEB128(Sym->getIndex(), W.OS);
+}
+
 MCSectionELF *ELFWriter::createRelocationSection(MCContext &Ctx,
                                                  const MCSectionELF &Sec) {
   if (OWriter.Relocations[&Sec].empty())
     return nullptr;
 
   const StringRef SectionName = Sec.getSectionName();
   std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
   RelaSectionName += SectionName;
void ELFWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
 
   case ELF::SHT_SYMTAB:
     sh_link = StringTableIndex;
     sh_info = LastLocalSymbolIndex;
     break;
 
   case ELF::SHT_SYMTAB_SHNDX:
   case ELF::SHT_LLVM_CALL_GRAPH_PROFILE:
+  case ELF::SHT_LLVM_ADDRSIG:
     sh_link = SymbolTableIndex;
     break;
 
   case ELF::SHT_GROUP:
     sh_link = SymbolTableIndex;
     sh_info = GroupSymbolIndex;
     break;
   }
for (MCSectionELF *Group : Groups) {
     SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
   }
 
   if (Mode == DwoOnly) {
     // dwo files don't have symbol tables or relocations, but they do have
     // string tables.
     StrTabBuilder.finalize();
   } else {
+    MCSectionELF *AddrsigSection;
+    if (OWriter.EmitAddrsigSection) {
+      AddrsigSection = Ctx.getELFSection(".llvm_addrsig", ELF::SHT_LLVM_ADDRSIG,
+                                         ELF::SHF_EXCLUDE);
+      addToSectionTable(AddrsigSection);
+    }
+
     // Compute symbol table information.
     computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
                        SectionOffsets);
 
     for (MCSectionELF *RelSection : Relocations) {
       align(RelSection->getAlignment());
 
       // Remember the offset into the file for this section.
       uint64_t SecStart = W.OS.tell();
 
       writeRelocations(Asm,
                        cast<MCSectionELF>(*RelSection->getAssociatedSection()));
 
       uint64_t SecEnd = W.OS.tell();
       SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
     }
+
+    if (OWriter.EmitAddrsigSection) {
+      uint64_t SecStart = W.OS.tell();
+      writeAddrsigSection();
+      uint64_t SecEnd = W.OS.tell();
+      SectionOffsets[AddrsigSection] = std::make_pair(SecStart, SecEnd);
+    }
   }
 
   if (CGProfileSection) {
     uint64_t SecStart = W.OS.tell();
     for (const MCAssembler::CGProfileEntry &CGPE : Asm.CGProfile) {
       W.write<uint32_t>(CGPE.From->getSymbol().getIndex());
       W.write<uint32_t>(CGPE.To->getSymbol().getIndex());
       W.write<uint64_t>(CGPE.Count);
if (Symbol.isUndefined() && Rest.startswith("@@") &&
       report_fatal_error("A @@ version cannot be undefined");
 
     if (Renames.count(&Symbol) && Renames[&Symbol] != Alias)
       report_fatal_error(llvm::Twine("Multiple symbol versions defined for ") +
                          Symbol.getName());
 
     Renames.insert(std::make_pair(&Symbol, Alias));
   }
+
+  for (const MCSymbol *&Sym : AddrsigSyms) {
+    if (const MCSymbol *R = Renames.lookup(cast<MCSymbolELF>(Sym)))
+      Sym = R;
+    Sym->setUsedInReloc();
+  }
 }
 
 // It is always valid to create a relocation with a symbol. It is preferable
 // to use a relocation with a section if that is possible. Using the section
 // allows us to omit some local symbols from the symbol table.
 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
                                                const MCSymbolRefExpr *RefA,
                                                const MCSymbolELF *Sym,

llvm/lib/MC/MCAsmStreamer.cpp

public:
 
   void EmitBundleAlignMode(unsigned AlignPow2) override;
   void EmitBundleLock(bool AlignToEnd) override;
   void EmitBundleUnlock() override;
 
   bool EmitRelocDirective(const MCExpr &Offset, StringRef Name,
                           const MCExpr *Expr, SMLoc Loc) override;
 
+  void EmitAddrsig() override;
+  void EmitAddrsigSym(const MCSymbol *Sym) override;
+
   /// If this file is backed by an assembly streamer, this dumps the specified
   /// string in the output .s file. This capability is indicated by the
   /// hasRawTextSupport() predicate.
   void EmitRawTextImpl(StringRef String) override;
 
   void FinishImpl() override;
 };
 
bool MCAsmStreamer::EmitRelocDirective(const MCExpr &Offset, StringRef Name,
   if (Expr) {
     OS << ", ";
     Expr->print(OS, MAI);
   }
   EmitEOL();
   return false;
 }
 
+void MCAsmStreamer::EmitAddrsig() {
+  OS << "\t.addrsig";
+  EmitEOL();
+}
+
+void MCAsmStreamer::EmitAddrsigSym(const MCSymbol *Sym) {
+  OS << "\t.addrsig_sym ";
+  Sym->print(OS, MAI);
+  EmitEOL();
+}
+
 /// EmitRawText - If this file is backed by an assembly streamer, this dumps
 /// the specified string in the output .s file.  This capability is
 /// indicated by the hasRawTextSupport() predicate.
 void MCAsmStreamer::EmitRawTextImpl(StringRef String) {
   if (!String.empty() && String.back() == '\n')
     String = String.substr(0, String.size()-1);
   OS << String;
   EmitEOL();

llvm/lib/MC/MCObjectStreamer.cpp

void MCObjectStreamer::emitFill(const MCExpr &NumValues, int64_t Size,
   assert(getCurrentSectionOnly() && "need a section");
   insert(new MCFillFragment(Expr, Size, NumValues, Loc));
 }
 
 void MCObjectStreamer::EmitFileDirective(StringRef Filename) {
   getAssembler().addFileName(Filename);
 }
 
+void MCObjectStreamer::EmitAddrsig() {
+  getAssembler().getWriter().emitAddrsigSection();
+}
+
+void MCObjectStreamer::EmitAddrsigSym(const MCSymbol *Sym) {
+  getAssembler().registerSymbol(*Sym);
+  getAssembler().getWriter().addAddrsigSymbol(Sym);
+}
+
 void MCObjectStreamer::FinishImpl() {
   // If we are generating dwarf for assembly source files dump out the sections.
   if (getContext().getGenDwarfForAssembly())
     MCGenDwarfInfo::Emit(this);
 
   // Dump out the dwarf file & directory tables and line tables.
   MCDwarfLineTable::Emit(this, getAssembler().getDWARFLinetableParams());
 
   flushPendingLabels(nullptr);
   getAssembler().Finish();
 }

llvm/lib/MC/MCParser/AsmParser.cpp

enum DirectiveKind {
     DK_ENDMACRO,
     DK_PURGEM,
     DK_SLEB128,
     DK_ULEB128,
     DK_ERR,
     DK_ERROR,
     DK_WARNING,
     DK_PRINT,
+    DK_ADDRSIG,
+    DK_ADDRSIG_SYM,
     DK_END
   };
 
   /// Maps directive name --> DirectiveKind enum, for
   /// directives parsed by this class.
   StringMap<DirectiveKind> DirectiveKindMap;
 
   // ".ascii", ".asciz", ".string"
private:
   bool parseDirectiveError(SMLoc DirectiveLoc, bool WithMessage);
 
   // ".warning"
   bool parseDirectiveWarning(SMLoc DirectiveLoc);
 
   // .print <double-quotes-string>
   bool parseDirectivePrint(SMLoc DirectiveLoc);
 
+  // Directives to support address-significance tables.
+  bool parseDirectiveAddrsig();
+  bool parseDirectiveAddrsigSym();
+
   void initializeDirectiveKindMap();
 };
 
 } // end anonymous namespace
 
 namespace llvm {
 
 extern MCAsmParserExtension *createDarwinAsmParser();
if (IDVal[0] == '.' && IDVal != ".") {
     case DK_DS_L:
     case DK_DS_S:
       return parseDirectiveDS(IDVal, 4);
     case DK_DS_P:
     case DK_DS_X:
       return parseDirectiveDS(IDVal, 12);
     case DK_PRINT:
       return parseDirectivePrint(IDLoc);
+    case DK_ADDRSIG:
+      return parseDirectiveAddrsig();
+    case DK_ADDRSIG_SYM:
+      return parseDirectiveAddrsigSym();
     }
 
     return Error(IDLoc, "unknown directive");
   }
 
   // __asm _emit or __asm __emit
   if (ParsingInlineAsm && (IDVal == "_emit" || IDVal == "__emit" ||
                            IDVal == "_EMIT" || IDVal == "__EMIT"))
void AsmParser::initializeDirectiveKindMap() {
   DirectiveKindMap[".ds.b"] = DK_DS_B;
   DirectiveKindMap[".ds.d"] = DK_DS_D;
   DirectiveKindMap[".ds.l"] = DK_DS_L;
   DirectiveKindMap[".ds.p"] = DK_DS_P;
   DirectiveKindMap[".ds.s"] = DK_DS_S;
   DirectiveKindMap[".ds.w"] = DK_DS_W;
   DirectiveKindMap[".ds.x"] = DK_DS_X;
   DirectiveKindMap[".print"] = DK_PRINT;
+  DirectiveKindMap[".addrsig"] = DK_ADDRSIG;
+  DirectiveKindMap[".addrsig_sym"] = DK_ADDRSIG_SYM;
 }
 
 MCAsmMacro *AsmParser::parseMacroLikeBody(SMLoc DirectiveLoc) {
   AsmToken EndToken, StartToken = getTok();
 
   unsigned NestLevel = 0;
   while (true) {
     // Check whether we have reached the end of the file.
bool AsmParser::parseDirectivePrint(SMLoc DirectiveLoc) {
   if (StrTok.isNot(AsmToken::String) || StrTok.getString().front() != '"')
     return Error(DirectiveLoc, "expected double quoted string after .print");
   if (parseToken(AsmToken::EndOfStatement, "expected end of statement"))
     return true;
   llvm::outs() << StrTok.getStringContents() << '\n';
   return false;
 }
 
+bool AsmParser::parseDirectiveAddrsig() {
+  getStreamer().EmitAddrsig();
+  return false;
+}
+
+bool AsmParser::parseDirectiveAddrsigSym() {
+  StringRef Name;
+  if (check(parseIdentifier(Name),
+            "expected identifier in '.addrsig_sym' directive"))
+    return true;
+  MCSymbol *Sym = getContext().getOrCreateSymbol(Name);
+  getStreamer().EmitAddrsigSym(Sym);
+  return false;
+}
+
 // We are comparing pointers, but the pointers are relative to a single string.
 // Thus, this should always be deterministic.
 static int rewritesSort(const AsmRewrite *AsmRewriteA,
                         const AsmRewrite *AsmRewriteB) {
   if (AsmRewriteA->Loc.getPointer() < AsmRewriteB->Loc.getPointer())
     return -1;
   if (AsmRewriteB->Loc.getPointer() < AsmRewriteA->Loc.getPointer())
     return 1;

llvm/lib/Object/ELF.cpp

switch (Type) {
     STRINGIFY_ENUM_CASE(ELF, SHT_PREINIT_ARRAY);
     STRINGIFY_ENUM_CASE(ELF, SHT_GROUP);
     STRINGIFY_ENUM_CASE(ELF, SHT_SYMTAB_SHNDX);
     STRINGIFY_ENUM_CASE(ELF, SHT_ANDROID_REL);
     STRINGIFY_ENUM_CASE(ELF, SHT_ANDROID_RELA);
     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_ODRTAB);
     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_LINKER_OPTIONS);
     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_CALL_GRAPH_PROFILE);
+    STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_ADDRSIG);
     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_ATTRIBUTES);
     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_HASH);
     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verdef);
     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verneed);
     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_versym);
   default:
     return "Unknown";
   }

llvm/lib/ObjectYAML/ELFYAML.cpp

#define ECase(X) IO.enumCase(Value, #X, ELF::X)
   ECase(SHT_GROUP);
   ECase(SHT_SYMTAB_SHNDX);
   ECase(SHT_LOOS);
   ECase(SHT_ANDROID_REL);
   ECase(SHT_ANDROID_RELA);
   ECase(SHT_LLVM_ODRTAB);
   ECase(SHT_LLVM_LINKER_OPTIONS);
   ECase(SHT_LLVM_CALL_GRAPH_PROFILE);
+  ECase(SHT_LLVM_ADDRSIG);
   ECase(SHT_GNU_ATTRIBUTES);
   ECase(SHT_GNU_HASH);
   ECase(SHT_GNU_verdef);
   ECase(SHT_GNU_verneed);
   ECase(SHT_GNU_versym);
   ECase(SHT_HIOS);
   ECase(SHT_LOPROC);
   switch (Object->Header.Machine) {

llvm/test/MC/ELF/addrsig-error.s

+// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - 2>&1 | FileCheck %s
+// CHECK: Undefined temporary symbol
+
+.addrsig
+.addrsig_sym .Lundef

llvm/test/MC/ELF/addrsig.s

+// RUN: llvm-mc -filetype=asm -triple x86_64-pc-linux-gnu %s -o - | FileCheck --check-prefix=ASM %s
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -s -t -sd -elf-addrsig | FileCheck %s
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -split-dwarf-file %t.dwo -o - | llvm-readobj -s -t -sd -elf-addrsig | FileCheck %s
+// RUN: llvm-readobj -s %t.dwo | FileCheck --check-prefix=DWO %s
+
+// CHECK:        Name: .llvm_addrsig
+// CHECK-NEXT:   Type: SHT_LLVM_ADDRSIG (0x6FFF4C03)
+// CHECK-NEXT:   Flags [ (0x80000000)
+// CHECK-NEXT:     SHF_EXCLUDE (0x80000000)
+// CHECK-NEXT:   ]
+// CHECK-NEXT:   Address:
+// CHECK-NEXT:   Offset:
+// CHECK-NEXT:   Size: 4
+// CHECK-NEXT:   Link: 4
+// CHECK-NEXT:   Info: 0
+// CHECK-NEXT:   AddressAlignment: 1
+// CHECK-NEXT:   EntrySize: 0
+// CHECK-NEXT:   SectionData (
+// CHECK-NEXT:     0000: 03050201
+// CHECK-NEXT:   )
+// CHECK-NEXT: }
+// CHECK-NEXT: Section {
+// CHECK-NEXT:   Index: 4
+// CHECK-NEXT:   Name: .symtab
+
+// CHECK:        Name: .Llocal
+// CHECK-NEXT:   Value:
+// CHECK-NEXT:   Size:
+// CHECK-NEXT:   Binding:
+// CHECK-NEXT:   Type:
+// CHECK-NEXT:   Other:
+// CHECK-NEXT:   Section:
+// CHECK-NEXT: }
+// CHECK-NEXT: Symbol {
+// CHECK-NEXT:   Name: local
+// CHECK-NEXT:   Value:
+// CHECK-NEXT:   Size:
+// CHECK-NEXT:   Binding:
+// CHECK-NEXT:   Type:
+// CHECK-NEXT:   Other:
+// CHECK-NEXT:   Section:
+// CHECK-NEXT: }
+// CHECK-NEXT: Symbol {
+// CHECK-NEXT:   Name: g1
+// CHECK-NEXT:   Value:
+// CHECK-NEXT:   Size:
+// CHECK-NEXT:   Binding:
+// CHECK-NEXT:   Type:
+// CHECK-NEXT:   Other:
+// CHECK-NEXT:   Section:
+// CHECK-NEXT: }
+// CHECK-NEXT: Symbol {
+// CHECK-NEXT:   Name: g2
+// CHECK-NEXT:   Value:
+// CHECK-NEXT:   Size:
+// CHECK-NEXT:   Binding:
+// CHECK-NEXT:   Type:
+// CHECK-NEXT:   Other:
+// CHECK-NEXT:   Section:
+// CHECK-NEXT: }
+// CHECK-NEXT: Symbol {
+// CHECK-NEXT:   Name: g3
+
+// CHECK:      Addrsig [
+// CHECK-NEXT:   Sym: g1 (3)
+// CHECK-NEXT:   Sym: g3 (5)
+// CHECK-NEXT:   Sym: local (2)
+// CHECK-NEXT:   Sym: .Llocal (1)
+// CHECK-NEXT: ]
+
+// ASM: .addrsig
+.addrsig
+// ASM: .addrsig_sym g1
+.addrsig_sym g1
+.globl g2
+// ASM: .addrsig_sym g3
+.addrsig_sym g3
+// ASM: .addrsig_sym local
+.addrsig_sym local
+// ASM: .addrsig_sym .Llocal
+.addrsig_sym .Llocal
+
+local:
+.Llocal:
+
+// DWO-NOT: .llvm_addrsig

llvm/tools/llvm-readobj/ELFDumper.cpp

 #include "llvm/Support/ARMAttributeParser.h"
 #include "llvm/Support/ARMBuildAttributes.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/FormattedStream.h"
+#include "llvm/Support/LEB128.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MipsABIFlags.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cinttypes>
 #include <cstddef>
 #include <cstdint>
public:
   void printMipsReginfo() override;
   void printMipsOptions() override;
 
   void printStackMap() const override;
 
   void printHashHistogram() override;
 
   void printCGProfile() override;
+  void printAddrsig() override;
 
   void printNotes() override;
 
   void printELFLinkerOptions() override;
 
 private:
   std::unique_ptr<DumpStyle<ELFT>> ELFDumperStyle;
 
private:
   DynRegionInfo DynSymRegion;
   DynRegionInfo DynamicTable;
   StringRef DynamicStringTable;
   StringRef SOName;
   const Elf_Hash *HashTable = nullptr;
   const Elf_GnuHash *GnuHashTable = nullptr;
   const Elf_Shdr *DotSymtabSec = nullptr;
   const Elf_Shdr *DotCGProfileSec = nullptr;
+  const Elf_Shdr *DotAddrsigSec = nullptr;
   StringRef DynSymtabName;
   ArrayRef<Elf_Word> ShndxTable;
 
   const Elf_Shdr *dot_gnu_version_sec = nullptr;   // .gnu.version
   const Elf_Shdr *dot_gnu_version_r_sec = nullptr; // .gnu.version_r
   const Elf_Shdr *dot_gnu_version_d_sec = nullptr; // .gnu.version_d
 
   // Records for each version index the corresponding Verdef or Vernaux entry.
public:
   void getSectionNameIndex(const Elf_Sym *Symbol, const Elf_Sym *FirstSym,
                            StringRef &SectionName,
                            unsigned &SectionIndex) const;
   StringRef getStaticSymbolName(uint32_t Index) const;
 
   void printSymbolsHelper(bool IsDynamic) const;
   const Elf_Shdr *getDotSymtabSec() const { return DotSymtabSec; }
   const Elf_Shdr *getDotCGProfileSec() const { return DotCGProfileSec; }
+  const Elf_Shdr *getDotAddrsigSec() const { return DotAddrsigSec; }
   ArrayRef<Elf_Word> getShndxTable() const { return ShndxTable; }
   StringRef getDynamicStringTable() const { return DynamicStringTable; }
   const DynRegionInfo &getDynRelRegion() const { return DynRelRegion; }
   const DynRegionInfo &getDynRelaRegion() const { return DynRelaRegion; }
   const DynRegionInfo &getDynPLTRelRegion() const { return DynPLTRelRegion; }
   const Elf_Hash *getHashTable() const { return HashTable; }
   const Elf_GnuHash *getGnuHashTable() const { return GnuHashTable; }
 };
public:
   virtual void printSymtabMessage(const ELFFile<ELFT> *obj, StringRef Name,
                                   size_t Offset) {}
   virtual void printSymbol(const ELFFile<ELFT> *Obj, const Elf_Sym *Symbol,
                            const Elf_Sym *FirstSym, StringRef StrTable,
                            bool IsDynamic) = 0;
   virtual void printProgramHeaders(const ELFFile<ELFT> *Obj) = 0;
   virtual void printHashHistogram(const ELFFile<ELFT> *Obj) = 0;
   virtual void printCGProfile(const ELFFile<ELFT> *Obj) = 0;
+  virtual void printAddrsig(const ELFFile<ELFT> *Obj) = 0;
   virtual void printNotes(const ELFFile<ELFT> *Obj) = 0;
   virtual void printELFLinkerOptions(const ELFFile<ELFT> *Obj) = 0;
   virtual void printMipsGOT(const MipsGOTParser<ELFT> &Parser) = 0;
   virtual void printMipsPLT(const MipsGOTParser<ELFT> &Parser) = 0;
   const ELFDumper<ELFT> *dumper() const { return Dumper; }
 
 private:
   const ELFDumper<ELFT> *Dumper;
public:
   void printSymbols(const ELFO *Obj) override;
   void printDynamicSymbols(const ELFO *Obj) override;
   void printDynamicRelocations(const ELFO *Obj) override;
   void printSymtabMessage(const ELFO *Obj, StringRef Name,
                           size_t Offset) override;
   void printProgramHeaders(const ELFO *Obj) override;
   void printHashHistogram(const ELFFile<ELFT> *Obj) override;
   void printCGProfile(const ELFFile<ELFT> *Obj) override;
+  void printAddrsig(const ELFFile<ELFT> *Obj) override;
   void printNotes(const ELFFile<ELFT> *Obj) override;
   void printELFLinkerOptions(const ELFFile<ELFT> *Obj) override;
   void printMipsGOT(const MipsGOTParser<ELFT> &Parser) override;
   void printMipsPLT(const MipsGOTParser<ELFT> &Parser) override;
 
 private:
   struct Field {
     StringRef Str;
public:
   void printRelocations(const Elf_Shdr *Sec, const ELFO *Obj);
   void printSections(const ELFO *Obj) override;
   void printSymbols(const ELFO *Obj) override;
   void printDynamicSymbols(const ELFO *Obj) override;
   void printDynamicRelocations(const ELFO *Obj) override;
   void printProgramHeaders(const ELFO *Obj) override;
   void printHashHistogram(const ELFFile<ELFT> *Obj) override;
   void printCGProfile(const ELFFile<ELFT> *Obj) override;
+  void printAddrsig(const ELFFile<ELFT> *Obj) override;
   void printNotes(const ELFFile<ELFT> *Obj) override;
   void printELFLinkerOptions(const ELFFile<ELFT> *Obj) override;
   void printMipsGOT(const MipsGOTParser<ELFT> &Parser) override;
   void printMipsPLT(const MipsGOTParser<ELFT> &Parser) override;
 
 private:
   void printRelocation(const ELFO *Obj, Elf_Rela Rel, const Elf_Shdr *SymTab);
   void printDynamicRelocation(const ELFO *Obj, Elf_Rela Rel);
case ELF::SHT_GNU_verneed:
       if (dot_gnu_version_r_sec != nullptr)
         reportError("Multiple SHT_GNU_verneed");
       dot_gnu_version_r_sec = &Sec;
       break;
     case ELF::SHT_LLVM_CALL_GRAPH_PROFILE:
       if (DotCGProfileSec != nullptr)
         reportError("Multiple .note.llvm.cgprofile");
       DotCGProfileSec = &Sec;
+      break;
+    case ELF::SHT_LLVM_ADDRSIG:
+      if (DotAddrsigSec != nullptr)
+        reportError("Multiple .llvm_addrsig");
+      DotAddrsigSec = &Sec;
+      break;
     }
   }
 
   parseDynamicTable(LoadSegments);
 
   if (opts::Output == opts::GNU)
     ELFDumperStyle.reset(new GNUStyle<ELFT>(Writer, this));
   else
template <class ELFT> void ELFDumper<ELFT>::printStackMap() const {
   prettyPrintStackMap(
       W, StackMapV2Parser<ELFT::TargetEndianness>(StackMapContentsArray));
 }
 
 template <class ELFT> void ELFDumper<ELFT>::printGroupSections() {
   ELFDumperStyle->printGroupSections(Obj);
 }
 
+template <class ELFT> void ELFDumper<ELFT>::printAddrsig() {
+  ELFDumperStyle->printAddrsig(Obj);
+}
+
 static inline void printFields(formatted_raw_ostream &OS, StringRef Str1,
                                StringRef Str2) {
   OS.PadToColumn(2u);
   OS << Str1;
   OS.PadToColumn(37u);
   OS << Str2 << "\n";
   OS.flush();
 }
std::string getSectionTypeString(unsigned Arch, unsigned Type) {
   case SHT_SYMTAB_SHNDX:
     return "SYMTAB SECTION INDICES";
   case SHT_LLVM_ODRTAB:
     return "LLVM_ODRTAB";
   case SHT_LLVM_LINKER_OPTIONS:
     return "LLVM_LINKER_OPTIONS";
   case SHT_LLVM_CALL_GRAPH_PROFILE:
     return "LLVM_CALL_GRAPH_PROFILE";
+  case SHT_LLVM_ADDRSIG:
+    return "LLVM_ADDRSIG";
   // FIXME: Parse processor specific GNU attributes
   case SHT_GNU_ATTRIBUTES:
     return "ATTRIBUTES";
   case SHT_GNU_HASH:
     return "GNU_HASH";
   case SHT_GNU_verdef:
     return "VERDEF";
   case SHT_GNU_verneed:
void GNUStyle<ELFT>::printHashHistogram(const ELFFile<ELFT> *Obj) {
   }
 }
 
 template <class ELFT>
 void GNUStyle<ELFT>::printCGProfile(const ELFFile<ELFT> *Obj) {
   OS << "GNUStyle::printCGProfile not implemented\n";
 }
 
+template <class ELFT>
+void GNUStyle<ELFT>::printAddrsig(const ELFFile<ELFT> *Obj) {
+    OS << "GNUStyle::printAddrsig not implemented\n";
+}
+
 static std::string getGNUNoteTypeName(const uint32_t NT) {
   static const struct {
     uint32_t ID;
     const char *Name;
   } Notes[] = {
       {ELF::NT_GNU_ABI_TAG, "NT_GNU_ABI_TAG (ABI version tag)"},
       {ELF::NT_GNU_HWCAP, "NT_GNU_HWCAP (DSO-supplied software HWCAP info)"},
       {ELF::NT_GNU_BUILD_ID, "NT_GNU_BUILD_ID (unique build ID bitstring)"},
W.printNumber("From", this->dumper()->getStaticSymbolName(CGPE.cgp_from),
                   CGPE.cgp_from);
     W.printNumber("To", this->dumper()->getStaticSymbolName(CGPE.cgp_to),
                   CGPE.cgp_to);
     W.printNumber("Weight", CGPE.cgp_weight);
   }
 }
 
 template <class ELFT>
+void LLVMStyle<ELFT>::printAddrsig(const ELFFile<ELFT> *Obj) {
+  ListScope L(W, "Addrsig");
+  if (!this->dumper()->getDotAddrsigSec())
+    return;
+  ArrayRef<uint8_t> Contents = unwrapOrError(
+      Obj->getSectionContents(this->dumper()->getDotAddrsigSec()));
+  const uint8_t *Cur = Contents.begin();
+  const uint8_t *End = Contents.end();
+  while (Cur != End) {
+    unsigned Size;
+    const char *Err;
+    uint64_t SymIndex = decodeULEB128(Cur, &Size, Contents.end(), &Err);
+    if (Err)
+      reportError(Err);
+    W.printNumber("Sym", this->dumper()->getStaticSymbolName(SymIndex),
+                  SymIndex);
+    Cur += Size;
+  }
+}
+
+template <class ELFT>
 void LLVMStyle<ELFT>::printNotes(const ELFFile<ELFT> *Obj) {
   W.startLine() << "printNotes not implemented!\n";
 }
 
 template <class ELFT>
 void LLVMStyle<ELFT>::printELFLinkerOptions(const ELFFile<ELFT> *Obj) {
   ListScope L(W, "LinkerOptions");
 

llvm/tools/llvm-readobj/ObjDumper.h

public:
   virtual void printProgramHeaders() { }
   virtual void printHashTable() { }
   virtual void printGnuHashTable() { }
   virtual void printLoadName() {}
   virtual void printVersionInfo() {}
   virtual void printGroupSections() {}
   virtual void printHashHistogram() {}
   virtual void printCGProfile() {}
+  virtual void printAddrsig() {}
   virtual void printNotes() {}
   virtual void printELFLinkerOptions() {}
 
   // Only implemented for ARM ELF at this time.
   virtual void printAttributes() { }
 
   // Only implemented for MIPS ELF at this time.
   virtual void printMipsPLTGOT() { }

llvm/tools/llvm-readobj/llvm-readobj.cpp

namespace opts {
   cl::opt<bool> HashHistogram(
       "elf-hash-histogram",
       cl::desc("Display bucket list histogram for hash sections"));
   cl::alias HashHistogramShort("I", cl::desc("Alias for -elf-hash-histogram"),
                                cl::aliasopt(HashHistogram));
 
   cl::opt<bool> CGProfile("elf-cg-profile", cl::desc("Display callgraph profile section"));
 
+  cl::opt<bool> Addrsig("elf-addrsig",
+                        cl::desc("Display address-significance table"));
+
   cl::opt<OutputStyleTy>
       Output("elf-output-style", cl::desc("Specify ELF dump style"),
              cl::values(clEnumVal(LLVM, "LLVM default style"),
                         clEnumVal(GNU, "GNU readelf style")),
              cl::init(LLVM));
 } // namespace opts
 
 namespace llvm {
if (isMipsArch(Obj->getArch())) {
         Dumper->printMipsOptions();
     }
     if (opts::SectionGroups)
       Dumper->printGroupSections();
     if (opts::HashHistogram)
       Dumper->printHashHistogram();
     if (opts::CGProfile)
       Dumper->printCGProfile();
+    if (opts::Addrsig)
+      Dumper->printAddrsig();
     if (opts::Notes)
       Dumper->printNotes();
   }
   if (Obj->isCOFF()) {
     if (opts::COFFImports)
       Dumper->printCOFFImports();
     if (opts::COFFExports)
       Dumper->printCOFFExports();