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      1 //===- llvm/MC/MCMachObjectWriter.h - Mach Object Writer --------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 
      9 #ifndef LLVM_MC_MCMACHOBJECTWRITER_H
     10 #define LLVM_MC_MCMACHOBJECTWRITER_H
     11 
     12 #include "llvm/ADT/DenseMap.h"
     13 #include "llvm/ADT/StringRef.h"
     14 #include "llvm/BinaryFormat/MachO.h"
     15 #include "llvm/MC/MCExpr.h"
     16 #include "llvm/MC/MCObjectWriter.h"
     17 #include "llvm/MC/MCSection.h"
     18 #include "llvm/MC/StringTableBuilder.h"
     19 #include "llvm/Support/EndianStream.h"
     20 #include <cstdint>
     21 #include <memory>
     22 #include <string>
     23 #include <vector>
     24 
     25 namespace llvm {
     26 
     27 class MachObjectWriter;
     28 
     29 class MCMachObjectTargetWriter : public MCObjectTargetWriter {
     30   const unsigned Is64Bit : 1;
     31   const uint32_t CPUType;
     32 protected:
     33   uint32_t CPUSubtype;
     34 public:
     35   unsigned LocalDifference_RIT;
     36 
     37 protected:
     38   MCMachObjectTargetWriter(bool Is64Bit_, uint32_t CPUType_,
     39                            uint32_t CPUSubtype_);
     40 
     41   void setLocalDifferenceRelocationType(unsigned Type) {
     42     LocalDifference_RIT = Type;
     43   }
     44 
     45 public:
     46   virtual ~MCMachObjectTargetWriter();
     47 
     48   Triple::ObjectFormatType getFormat() const override { return Triple::MachO; }
     49   static bool classof(const MCObjectTargetWriter *W) {
     50     return W->getFormat() == Triple::MachO;
     51   }
     52 
     53   /// \name Lifetime Management
     54   /// @{
     55 
     56   virtual void reset() {}
     57 
     58   /// @}
     59 
     60   /// \name Accessors
     61   /// @{
     62 
     63   bool is64Bit() const { return Is64Bit; }
     64   uint32_t getCPUType() const { return CPUType; }
     65   uint32_t getCPUSubtype() const { return CPUSubtype; }
     66   unsigned getLocalDifferenceRelocationType() const {
     67     return LocalDifference_RIT;
     68   }
     69 
     70   /// @}
     71 
     72   /// \name API
     73   /// @{
     74 
     75   virtual void recordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
     76                                 const MCAsmLayout &Layout,
     77                                 const MCFragment *Fragment,
     78                                 const MCFixup &Fixup, MCValue Target,
     79                                 uint64_t &FixedValue) = 0;
     80 
     81   /// @}
     82 };
     83 
     84 class MachObjectWriter : public MCObjectWriter {
     85   /// Helper struct for containing some precomputed information on symbols.
     86   struct MachSymbolData {
     87     const MCSymbol *Symbol;
     88     uint64_t StringIndex;
     89     uint8_t SectionIndex;
     90 
     91     // Support lexicographic sorting.
     92     bool operator<(const MachSymbolData &RHS) const;
     93   };
     94 
     95   /// The target specific Mach-O writer instance.
     96   std::unique_ptr<MCMachObjectTargetWriter> TargetObjectWriter;
     97 
     98   /// \name Relocation Data
     99   /// @{
    100 
    101   struct RelAndSymbol {
    102     const MCSymbol *Sym;
    103     MachO::any_relocation_info MRE;
    104     RelAndSymbol(const MCSymbol *Sym, const MachO::any_relocation_info &MRE)
    105         : Sym(Sym), MRE(MRE) {}
    106   };
    107 
    108   DenseMap<const MCSection *, std::vector<RelAndSymbol>> Relocations;
    109   DenseMap<const MCSection *, unsigned> IndirectSymBase;
    110 
    111   SectionAddrMap SectionAddress;
    112 
    113   /// @}
    114   /// \name Symbol Table Data
    115   /// @{
    116 
    117   StringTableBuilder StringTable;
    118   std::vector<MachSymbolData> LocalSymbolData;
    119   std::vector<MachSymbolData> ExternalSymbolData;
    120   std::vector<MachSymbolData> UndefinedSymbolData;
    121 
    122   /// @}
    123 
    124   MachSymbolData *findSymbolData(const MCSymbol &Sym);
    125 
    126   void writeWithPadding(StringRef Str, uint64_t Size);
    127 
    128 public:
    129   MachObjectWriter(std::unique_ptr<MCMachObjectTargetWriter> MOTW,
    130                    raw_pwrite_stream &OS, bool IsLittleEndian)
    131       : TargetObjectWriter(std::move(MOTW)),
    132         StringTable(TargetObjectWriter->is64Bit() ? StringTableBuilder::MachO64
    133                                                   : StringTableBuilder::MachO),
    134         W(OS, IsLittleEndian ? support::little : support::big) {}
    135 
    136   support::endian::Writer W;
    137 
    138   const MCSymbol &findAliasedSymbol(const MCSymbol &Sym) const;
    139 
    140   /// \name Lifetime management Methods
    141   /// @{
    142 
    143   void reset() override;
    144 
    145   /// @}
    146 
    147   /// \name Utility Methods
    148   /// @{
    149 
    150   bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
    151 
    152   SectionAddrMap &getSectionAddressMap() { return SectionAddress; }
    153 
    154   uint64_t getSectionAddress(const MCSection *Sec) const {
    155     return SectionAddress.lookup(Sec);
    156   }
    157   uint64_t getSymbolAddress(const MCSymbol &S, const MCAsmLayout &Layout) const;
    158 
    159   uint64_t getFragmentAddress(const MCFragment *Fragment,
    160                               const MCAsmLayout &Layout) const;
    161 
    162   uint64_t getPaddingSize(const MCSection *SD, const MCAsmLayout &Layout) const;
    163 
    164   bool doesSymbolRequireExternRelocation(const MCSymbol &S);
    165 
    166   /// @}
    167 
    168   /// \name Target Writer Proxy Accessors
    169   /// @{
    170 
    171   bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
    172   bool isX86_64() const {
    173     uint32_t CPUType = TargetObjectWriter->getCPUType();
    174     return CPUType == MachO::CPU_TYPE_X86_64;
    175   }
    176 
    177   /// @}
    178 
    179   void writeHeader(MachO::HeaderFileType Type, unsigned NumLoadCommands,
    180                    unsigned LoadCommandsSize, bool SubsectionsViaSymbols);
    181 
    182   /// Write a segment load command.
    183   ///
    184   /// \param NumSections The number of sections in this segment.
    185   /// \param SectionDataSize The total size of the sections.
    186   void writeSegmentLoadCommand(StringRef Name, unsigned NumSections,
    187                                uint64_t VMAddr, uint64_t VMSize,
    188                                uint64_t SectionDataStartOffset,
    189                                uint64_t SectionDataSize, uint32_t MaxProt,
    190                                uint32_t InitProt);
    191 
    192   void writeSection(const MCAsmLayout &Layout, const MCSection &Sec,
    193                     uint64_t VMAddr, uint64_t FileOffset, unsigned Flags,
    194                     uint64_t RelocationsStart, unsigned NumRelocations);
    195 
    196   void writeSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
    197                               uint32_t StringTableOffset,
    198                               uint32_t StringTableSize);
    199 
    200   void writeDysymtabLoadCommand(
    201       uint32_t FirstLocalSymbol, uint32_t NumLocalSymbols,
    202       uint32_t FirstExternalSymbol, uint32_t NumExternalSymbols,
    203       uint32_t FirstUndefinedSymbol, uint32_t NumUndefinedSymbols,
    204       uint32_t IndirectSymbolOffset, uint32_t NumIndirectSymbols);
    205 
    206   void writeNlist(MachSymbolData &MSD, const MCAsmLayout &Layout);
    207 
    208   void writeLinkeditLoadCommand(uint32_t Type, uint32_t DataOffset,
    209                                 uint32_t DataSize);
    210 
    211   void writeLinkerOptionsLoadCommand(const std::vector<std::string> &Options);
    212 
    213   // FIXME: We really need to improve the relocation validation. Basically, we
    214   // want to implement a separate computation which evaluates the relocation
    215   // entry as the linker would, and verifies that the resultant fixup value is
    216   // exactly what the encoder wanted. This will catch several classes of
    217   // problems:
    218   //
    219   //  - Relocation entry bugs, the two algorithms are unlikely to have the same
    220   //    exact bug.
    221   //
    222   //  - Relaxation issues, where we forget to relax something.
    223   //
    224   //  - Input errors, where something cannot be correctly encoded. 'as' allows
    225   //    these through in many cases.
    226 
    227   // Add a relocation to be output in the object file. At the time this is
    228   // called, the symbol indexes are not know, so if the relocation refers
    229   // to a symbol it should be passed as \p RelSymbol so that it can be updated
    230   // afterwards. If the relocation doesn't refer to a symbol, nullptr should be
    231   // used.
    232   void addRelocation(const MCSymbol *RelSymbol, const MCSection *Sec,
    233                      MachO::any_relocation_info &MRE) {
    234     RelAndSymbol P(RelSymbol, MRE);
    235     Relocations[Sec].push_back(P);
    236   }
    237 
    238   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
    239                         const MCFragment *Fragment, const MCFixup &Fixup,
    240                         MCValue Target, uint64_t &FixedValue) override;
    241 
    242   void bindIndirectSymbols(MCAssembler &Asm);
    243 
    244   /// Compute the symbol table data.
    245   void computeSymbolTable(MCAssembler &Asm,
    246                           std::vector<MachSymbolData> &LocalSymbolData,
    247                           std::vector<MachSymbolData> &ExternalSymbolData,
    248                           std::vector<MachSymbolData> &UndefinedSymbolData);
    249 
    250   void computeSectionAddresses(const MCAssembler &Asm,
    251                                const MCAsmLayout &Layout);
    252 
    253   void executePostLayoutBinding(MCAssembler &Asm,
    254                                 const MCAsmLayout &Layout) override;
    255 
    256   bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
    257                                               const MCSymbol &A,
    258                                               const MCSymbol &B,
    259                                               bool InSet) const override;
    260 
    261   bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
    262                                               const MCSymbol &SymA,
    263                                               const MCFragment &FB, bool InSet,
    264                                               bool IsPCRel) const override;
    265 
    266   uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
    267 };
    268 
    269 /// Construct a new Mach-O writer instance.
    270 ///
    271 /// This routine takes ownership of the target writer subclass.
    272 ///
    273 /// \param MOTW - The target specific Mach-O writer subclass.
    274 /// \param OS - The stream to write to.
    275 /// \returns The constructed object writer.
    276 std::unique_ptr<MCObjectWriter>
    277 createMachObjectWriter(std::unique_ptr<MCMachObjectTargetWriter> MOTW,
    278                        raw_pwrite_stream &OS, bool IsLittleEndian);
    279 
    280 } // end namespace llvm
    281 
    282 #endif // LLVM_MC_MCMACHOBJECTWRITER_H
    283