[MC] Error on a .zerofill directive in a non-virtual section

[thegameg]

Summary

On darwin, all virtual sections have zerofill type, and having a .zerofill directive in a non-virtual section is not allowed. Instead of asserting, show a nicer error.

In order to use the equivalent of .zerofill in a non-virtual section, the usage of .zero of .space is required.

This patch replaces the assert with an error.

[thegameg]

Ping?

[pete]

Sorry for the delay. LGTM.

[thegameg]

Thanks @pete !

include/llvm/MC/MCELFStreamer.h

public:
   void emitELFSize(MCSymbol *Symbol, const MCExpr *Value) override;
   void emitELFSymverDirective(StringRef AliasName,
                               const MCSymbol *Aliasee) override;
 
   void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                              unsigned ByteAlignment) override;
 
   void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
-                    uint64_t Size = 0, unsigned ByteAlignment = 0) override;
+                    uint64_t Size = 0, unsigned ByteAlignment = 0,
+                    SMLoc L = SMLoc()) override;
   void EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
                       unsigned ByteAlignment = 0) override;
   void EmitValueImpl(const MCExpr *Value, unsigned Size,
                      SMLoc Loc = SMLoc()) override;
 
   void EmitIdent(StringRef IdentString) override;
 
   void EmitValueToAlignment(unsigned, int64_t, unsigned, unsigned) override;

include/llvm/MC/MCStreamer.h

public:
   /// Emit the zerofill section and an optional symbol.
   ///
   /// \param Section - The zerofill section to create and or to put the symbol
   /// \param Symbol - The zerofill symbol to emit, if non-NULL.
   /// \param Size - The size of the zerofill symbol.
   /// \param ByteAlignment - The alignment of the zerofill symbol if
   /// non-zero. This must be a power of 2 on some targets.
   virtual void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
-                            uint64_t Size = 0, unsigned ByteAlignment = 0) = 0;
+                            uint64_t Size = 0, unsigned ByteAlignment = 0,
+                            SMLoc Loc = SMLoc()) = 0;
 
   /// Emit a thread local bss (.tbss) symbol.
   ///
   /// \param Section - The thread local common section.
   /// \param Symbol - The thread local common symbol to emit.
   /// \param Size - The size of the symbol.
   /// \param ByteAlignment - The alignment of the thread local common symbol
   /// if non-zero.  This must be a power of 2 on some targets.

include/llvm/MC/MCWasmStreamer.h

void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                         unsigned ByteAlignment) override;
 
   void emitELFSize(MCSymbol *Symbol, const MCExpr *Value) override;
 
   void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                              unsigned ByteAlignment) override;
 
   void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
-                    uint64_t Size = 0, unsigned ByteAlignment = 0) override;
+                    uint64_t Size = 0, unsigned ByteAlignment = 0,
+                    SMLoc Loc = SMLoc()) override;
   void EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
                       unsigned ByteAlignment = 0) override;
   void EmitValueImpl(const MCExpr *Value, unsigned Size,
                      SMLoc Loc = SMLoc()) override;
 
   void EmitIdent(StringRef IdentString) override;
 
   void EmitValueToAlignment(unsigned, int64_t, unsigned, unsigned) override;

include/llvm/MC/MCWinCOFFStreamer.h

public:
   void EmitCOFFSymbolIndex(MCSymbol const *Symbol) override;
   void EmitCOFFSectionIndex(MCSymbol const *Symbol) override;
   void EmitCOFFSecRel32(MCSymbol const *Symbol, uint64_t Offset) override;
   void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                         unsigned ByteAlignment) override;
   void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                              unsigned ByteAlignment) override;
   void EmitZerofill(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
-                    unsigned ByteAlignment) override;
+                    unsigned ByteAlignment, SMLoc Loc = SMLoc()) override;
   void EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
                       unsigned ByteAlignment) override;
   void EmitIdent(StringRef IdentString) override;
   void EmitWinEHHandlerData(SMLoc Loc) override;
   void FinishImpl() override;
 
   /// \}
 

lib/MC/MCAsmStreamer.cpp

public:
   ///
   /// @param Symbol - The common symbol to emit.
   /// @param Size - The size of the common symbol.
   /// @param ByteAlignment - The alignment of the common symbol in bytes.
   void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                              unsigned ByteAlignment) override;
 
   void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
-                    uint64_t Size = 0, unsigned ByteAlignment = 0) override;
+                    uint64_t Size = 0, unsigned ByteAlignment = 0,
+                    SMLoc Loc = SMLoc()) override;
 
   void EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
                       unsigned ByteAlignment = 0) override;
 
   void EmitBinaryData(StringRef Data) override;
 
   void EmitBytes(StringRef Data) override;
 
case LCOMM::Log2Alignment:
       OS << ',' << Log2_32(ByteAlign);
       break;
     }
   }
   EmitEOL();
 }
 
 void MCAsmStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
-                                 uint64_t Size, unsigned ByteAlignment) {
+                                 uint64_t Size, unsigned ByteAlignment,
+                                 SMLoc Loc) {
   if (Symbol)
     AssignFragment(Symbol, &Section->getDummyFragment());
 
   // Note: a .zerofill directive does not switch sections.
   OS << ".zerofill ";
 
+  assert(Section->getVariant() == MCSection::SV_MachO &&
+         ".zerofill is a Mach-O specific directive");
   // This is a mach-o specific directive.
+
   const MCSectionMachO *MOSection = ((const MCSectionMachO*)Section);
   OS << MOSection->getSegmentName() << "," << MOSection->getSectionName();
 
   if (Symbol) {
     OS << ',';
     Symbol->print(OS, MAI);
     OS << ',' << Size;
     if (ByteAlignment != 0)
       OS << ',' << Log2_32(ByteAlignment);
   }
   EmitEOL();
 }
 
 // .tbss sym, size, align
 // This depends that the symbol has already been mangled from the original,
 // e.g. _a.
 void MCAsmStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
                                    uint64_t Size, unsigned ByteAlignment) {
   AssignFragment(Symbol, &Section->getDummyFragment());
 
   assert(Symbol && "Symbol shouldn't be NULL!");
   // Instead of using the Section we'll just use the shortcut.
+
+  assert(Section->getVariant() == MCSection::SV_MachO &&
+         ".zerofill is a Mach-O specific directive");
   // This is a mach-o specific directive and section.
+
   OS << ".tbss ";
   Symbol->print(OS, MAI);
   OS << ", " << Size;
 
   // Output align if we have it.  We default to 1 so don't bother printing
   // that.
   if (ByteAlignment > 1) OS << ", " << Log2_32(ByteAlignment);
 

lib/MC/MCELFStreamer.cpp

void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
   llvm_unreachable("Generic ELF doesn't support this directive");
 }
 
 void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
   llvm_unreachable("ELF doesn't support this directive");
 }
 
 void MCELFStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
-                                 uint64_t Size, unsigned ByteAlignment) {
+                                 uint64_t Size, unsigned ByteAlignment,
+                                 SMLoc Loc) {
   llvm_unreachable("ELF doesn't support this directive");
 }
 
 void MCELFStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
                                    uint64_t Size, unsigned ByteAlignment) {
   llvm_unreachable("ELF doesn't support this directive");
 }
 

lib/MC/MCMachOStreamer.cpp

public:
   bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
   void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) override;
   void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                         unsigned ByteAlignment) override;
 
   void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                              unsigned ByteAlignment) override;
   void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
-                    uint64_t Size = 0, unsigned ByteAlignment = 0) override;
+                    uint64_t Size = 0, unsigned ByteAlignment = 0,
+                    SMLoc Loc = SMLoc()) override;
   void EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
                       unsigned ByteAlignment = 0) override;
 
   void EmitIdent(StringRef IdentString) override {
     llvm_unreachable("macho doesn't support this directive");
   }
 
   void EmitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) override {

 void MCMachOStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                             unsigned ByteAlignment) {
   // '.lcomm' is equivalent to '.zerofill'.
   return EmitZerofill(getContext().getObjectFileInfo()->getDataBSSSection(),
                       Symbol, Size, ByteAlignment);
 }
 
 void MCMachOStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
-                                   uint64_t Size, unsigned ByteAlignment) {
-  // On darwin all virtual sections have zerofill type.
-  assert(Section->isVirtualSection() && "Section does not have zerofill type!");
+                                   uint64_t Size, unsigned ByteAlignment,
+                                   SMLoc Loc) {
+  // On darwin all virtual sections have zerofill type. Disallow the usage of
+  // .zerofill in non-virtual functions. If something similar is needed, use
+  // .space or .zero.
+  if (!Section->isVirtualSection()) {
+    getContext().reportError(
+        Loc, "The usage of .zerofill is restricted to sections of "
+             "ZEROFILL type. Use .zero or .space instead.");
+    return; // Early returning here shouldn't harm. EmitZeros should work on any
+            // section.
+  }
 
   PushSection();
   SwitchSection(Section);
 
   // The symbol may not be present, which only creates the section.
   if (Symbol) {
     EmitValueToAlignment(ByteAlignment, 0, 1, 0);
     EmitLabel(Symbol);

lib/MC/MCNullStreamer.cpp

public:
     bool EmitSymbolAttribute(MCSymbol *Symbol,
                              MCSymbolAttr Attribute) override {
       return true;
     }
 
     void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                           unsigned ByteAlignment) override {}
     void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
-                      uint64_t Size = 0, unsigned ByteAlignment = 0) override {}
+                      uint64_t Size = 0, unsigned ByteAlignment = 0,
+                      SMLoc Loc = SMLoc()) override {}
     void EmitGPRel32Value(const MCExpr *Value) override {}
     void BeginCOFFSymbolDef(const MCSymbol *Symbol) override {}
     void EmitCOFFSymbolStorageClass(int StorageClass) override {}
     void EmitCOFFSymbolType(int Type) override {}
     void EndCOFFSymbolDef() override {}
   };
 
 }
 
 MCStreamer *llvm::createNullStreamer(MCContext &Context) {
   return new MCNullStreamer(Context);
 }

lib/MC/MCParser/DarwinAsmParser.cpp

bool DarwinAsmParser::parseDirectiveZerofill(StringRef, SMLoc) {
   if (getParser().parseIdentifier(Segment))
     return TokError("expected segment name after '.zerofill' directive");
 
   if (getLexer().isNot(AsmToken::Comma))
     return TokError("unexpected token in directive");
   Lex();
 
   StringRef Section;
+  SMLoc SectionLoc = getLexer().getLoc();
   if (getParser().parseIdentifier(Section))
     return TokError("expected section name after comma in '.zerofill' "
                     "directive");
 
   // If this is the end of the line all that was wanted was to create the
   // the section but with no symbol.
   if (getLexer().is(AsmToken::EndOfStatement)) {
     // Create the zerofill section but no symbol
-    getStreamer().EmitZerofill(getContext().getMachOSection(
-                                 Segment, Section, MachO::S_ZEROFILL,
-                                 0, SectionKind::getBSS()));
+    getStreamer().EmitZerofill(
+        getContext().getMachOSection(Segment, Section, MachO::S_ZEROFILL, 0,
+                                     SectionKind::getBSS()),
+        /*Symbol=*/nullptr, /*Size=*/0, /*ByteAlignment=*/0, SectionLoc);
     return false;
   }
 
   if (getLexer().isNot(AsmToken::Comma))
     return TokError("unexpected token in directive");
   Lex();
 
   SMLoc IDLoc = getLexer().getLoc();
if (!Sym->isUndefined())
     return Error(IDLoc, "invalid symbol redefinition");
 
   // Create the zerofill Symbol with Size and Pow2Alignment
   //
   // FIXME: Arch specific.
   getStreamer().EmitZerofill(getContext().getMachOSection(
                                Segment, Section, MachO::S_ZEROFILL,
                                0, SectionKind::getBSS()),
-                             Sym, Size, 1 << Pow2Alignment);
+                             Sym, Size, 1 << Pow2Alignment, SectionLoc);
 
   return false;
 }
 
 /// ParseDirectiveDataRegion
 ///  ::= .data_region [ ( jt8 | jt16 | jt32 ) ]
 bool DarwinAsmParser::parseDirectiveDataRegion(StringRef, SMLoc) {
   if (getLexer().is(AsmToken::EndOfStatement)) {

lib/MC/MCWasmStreamer.cpp

void MCWasmStreamer::EmitThumbFunc(MCSymbol *Func) {
   llvm_unreachable("Generic Wasm doesn't support this directive");
 }
 
 void MCWasmStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
   llvm_unreachable("Wasm doesn't support this directive");
 }
 
 void MCWasmStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
-                                  uint64_t Size, unsigned ByteAlignment) {
+                                  uint64_t Size, unsigned ByteAlignment,
+                                  SMLoc Loc) {
   llvm_unreachable("Wasm doesn't support this directive");
 }
 
 void MCWasmStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
                                     uint64_t Size, unsigned ByteAlignment) {
   llvm_unreachable("Wasm doesn't support this directive");
 }

lib/MC/MCWinCOFFStreamer.cpp

void MCWinCOFFStreamer::EmitLocalCommonSymbol(MCSymbol *S, uint64_t Size,
   EmitValueToAlignment(ByteAlignment, 0, 1, 0);
   EmitLabel(Symbol);
   Symbol->setExternal(false);
   EmitZeros(Size);
   PopSection();
 }
 
 void MCWinCOFFStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
-                                     uint64_t Size, unsigned ByteAlignment) {
+                                     uint64_t Size, unsigned ByteAlignment,
+                                     SMLoc Loc) {
   llvm_unreachable("not implemented");
 }
 
 void MCWinCOFFStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
                                        uint64_t Size, unsigned ByteAlignment) {
   llvm_unreachable("not implemented");
 }
 

lib/Object/RecordStreamer.h

public:
   RecordStreamer(MCContext &Context, const Module &M);
 
   void EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
                        bool) override;
   void EmitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc()) override;
   void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) override;
   bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
   void EmitZerofill(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
-                    unsigned ByteAlignment) override;
+                    unsigned ByteAlignment, SMLoc Loc = SMLoc()) override;
   void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                         unsigned ByteAlignment) override;
   /// Record .symver aliases for later processing.
   void emitELFSymverDirective(StringRef AliasName,
                               const MCSymbol *Aliasee) override;
 
   // Emit ELF .symver aliases and ensure they have the same binding as the
   // defined symbol they alias with.

lib/Object/RecordStreamer.cpp

bool RecordStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
   if (Attribute == MCSA_Global || Attribute == MCSA_Weak)
     markGlobal(*Symbol, Attribute);
   if (Attribute == MCSA_LazyReference)
     markUsed(*Symbol);
   return true;
 }
 
 void RecordStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
-                                  uint64_t Size, unsigned ByteAlignment) {
+                                  uint64_t Size, unsigned ByteAlignment,
+                                  SMLoc Loc) {
   markDefined(*Symbol);
 }
 
 void RecordStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                       unsigned ByteAlignment) {
   markDefined(*Symbol);
 }
 

test/MC/MachO/zero-space.s

+// RUN: llvm-mc -triple x86_64-apple-darwin9 %s -filetype=obj -o - | llvm-readobj -file-headers -s -sd -r -t --macho-segment --macho-dysymtab --macho-indirect-symbols | FileCheck %s
+
+        .const
+        .p2align 6
+        Lzero:
+          .space 64
+          .zero 64
+
+// CHECK: File: <stdin>
+// CHECK-NEXT: Format: Mach-O 64-bit x86-64
+// CHECK-NEXT: Arch: x86_64
+// CHECK-NEXT: AddressSize: 64bit
+// CHECK-NEXT: MachHeader {
+// CHECK-NEXT:   Magic: Magic64 (0xFEEDFACF)
+// CHECK-NEXT:   CpuType: X86-64 (0x1000007)
+// CHECK-NEXT:   CpuSubType: CPU_SUBTYPE_X86_64_ALL (0x3)
+// CHECK-NEXT:   FileType: Relocatable (0x1)
+// CHECK-NEXT:   NumOfLoadCommands: 2
+// CHECK-NEXT:   SizeOfLoadCommands: 248
+// CHECK-NEXT:   Flags [ (0x0)
+// CHECK-NEXT:   ]
+// CHECK-NEXT:   Reserved: 0x0
+// CHECK-NEXT: }
+// CHECK-NEXT: Sections [
+// CHECK-NEXT:   Section {
+// CHECK-NEXT:     Index: 0
+// CHECK-NEXT:     Name: __text (5F 5F 74 65 78 74 00 00 00 00 00 00 00 00 00 00)
+// CHECK-NEXT:     Segment: __TEXT (5F 5F 54 45 58 54 00 00 00 00 00 00 00 00 00 00)
+// CHECK-NEXT:     Address: 0x0
+// CHECK-NEXT:     Size: 0x0
+// CHECK-NEXT:     Offset: 280
+// CHECK-NEXT:     Alignment: 0
+// CHECK-NEXT:     RelocationOffset: 0x0
+// CHECK-NEXT:     RelocationCount: 0
+// CHECK-NEXT:     Type: 0x0
+// CHECK-NEXT:     Attributes [ (0x800000)
+// CHECK-NEXT:       PureInstructions (0x800000)
+// CHECK-NEXT:     ]
+// CHECK-NEXT:     Reserved1: 0x0
+// CHECK-NEXT:     Reserved2: 0x0
+// CHECK-NEXT:     Reserved3: 0x0
+// CHECK-NEXT:     SectionData (
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Section {
+// CHECK-NEXT:     Index: 1
+// CHECK-NEXT:     Name: __const (5F 5F 63 6F 6E 73 74 00 00 00 00 00 00 00 00 00)
+// CHECK-NEXT:     Segment: __TEXT (5F 5F 54 45 58 54 00 00 00 00 00 00 00 00 00 00)
+// CHECK-NEXT:     Address: 0x0
+// CHECK-NEXT:     Size: 0x80
+// CHECK-NEXT:     Offset: 280
+// CHECK-NEXT:     Alignment: 6
+// CHECK-NEXT:     RelocationOffset: 0x0
+// CHECK-NEXT:     RelocationCount: 0
+// CHECK-NEXT:     Type: 0x0
+// CHECK-NEXT:     Attributes [ (0x0)
+// CHECK-NEXT:     ]
+// CHECK-NEXT:     Reserved1: 0x0
+// CHECK-NEXT:     Reserved2: 0x0
+// CHECK-NEXT:     Reserved3: 0x0
+// CHECK-NEXT:     SectionData (
+// CHECK-NEXT:       0000: 00000000 00000000 00000000 00000000  |................|
+// CHECK-NEXT:       0010: 00000000 00000000 00000000 00000000  |................|
+// CHECK-NEXT:       0020: 00000000 00000000 00000000 00000000  |................|
+// CHECK-NEXT:       0030: 00000000 00000000 00000000 00000000  |................|
+// CHECK-NEXT:       0040: 00000000 00000000 00000000 00000000  |................|
+// CHECK-NEXT:       0050: 00000000 00000000 00000000 00000000  |................|
+// CHECK-NEXT:       0060: 00000000 00000000 00000000 00000000  |................|
+// CHECK-NEXT:       0070: 00000000 00000000 00000000 00000000  |................|
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+// CHECK-NEXT: Relocations [
+// CHECK-NEXT: ]
+// CHECK-NEXT: Symbols [
+// CHECK-NEXT: ]
+// CHECK-NEXT: Segment {
+// CHECK-NEXT:   Cmd: LC_SEGMENT_64
+// CHECK-NEXT:   Name:
+// CHECK-NEXT:   Size: 232
+// CHECK-NEXT:   vmaddr: 0x0
+// CHECK-NEXT:   vmsize: 0x80
+// CHECK-NEXT:   fileoff: 280
+// CHECK-NEXT:   filesize: 128
+// CHECK-NEXT:   maxprot: rwx
+// CHECK-NEXT:   initprot: rwx
+// CHECK-NEXT:   nsects: 2
+// CHECK-NEXT:   flags: 0x0
+// CHECK-NEXT: }

test/MC/MachO/zerofill-text.s

+// RUN: not llvm-mc -triple x86_64-apple-darwin9 %s -filetype=obj -o /dev/null 2>&1 | FileCheck %s
+
+        .text
+        .zerofill __TEXT, __const, zfill, 2, 1
+
+// CHECK: 6:33: error: The usage of .zerofill is restricted to sections of ZEROFILL type. Use .zero or .space instead.
+// CHECK-NEXT: .zerofill __TEXT, __const, zfill, 2, 1

tools/llvm-mca/llvm-mca.cpp

public:
 
   bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override {
     return true;
   }
 
   void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                         unsigned ByteAlignment) override {}
   void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
-                    uint64_t Size = 0, unsigned ByteAlignment = 0) override {}
+                    uint64_t Size = 0, unsigned ByteAlignment = 0,
+                    SMLoc Loc = SMLoc()) override {}
   void EmitGPRel32Value(const MCExpr *Value) override {}
   void BeginCOFFSymbolDef(const MCSymbol *Symbol) override {}
   void EmitCOFFSymbolStorageClass(int StorageClass) override {}
   void EmitCOFFSymbolType(int Type) override {}
   void EndCOFFSymbolDef() override {}
 
   const std::vector<std::unique_ptr<const MCInst>> &
   GetInstructionSequence(unsigned Index) const {