lib/CodeGen/ELFWriter.h

   1 //===-- ELFWriter.h - Target-independent ELF writer support -----*- C++ -*-===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file defines the ELFWriter class.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef ELFWRITER_H
  15 #define ELFWRITER_H
  16
  17 #include "llvm/ADT/SetVector.h"
  18 #include "llvm/CodeGen/MachineFunctionPass.h"
  19 #include <map>
  20
  21 namespace llvm {
  22   class BinaryObject;
  23   class Constant;
  24   class ConstantStruct;
  25   class ELFCodeEmitter;
  26   class ELFRelocation;
  27   class ELFSection;
  28   struct ELFSym;
  29   class GlobalVariable;
  30   class Mangler;
  31   class MachineCodeEmitter;
  32   class MachineConstantPoolEntry;
  33   class ObjectCodeEmitter;
  34   class TargetAsmInfo;
  35   class TargetELFWriterInfo;
  36   class raw_ostream;
  37   class SectionKind;
  38   class MCContext;
  39
  40   typedef std::vector<ELFSym*>::iterator ELFSymIter;
  41   typedef std::vector<ELFSection*>::iterator ELFSectionIter;
  42   typedef SetVector<const GlobalValue*>::const_iterator PendingGblsIter;
  43   typedef SetVector<const char *>::const_iterator PendingExtsIter;
  44
  45   /// ELFWriter - This class implements the common target-independent code for
  46   /// writing ELF files.  Targets should derive a class from this to
  47   /// parameterize the output format.
  48   ///
  49   class ELFWriter : public MachineFunctionPass {
  50     friend class ELFCodeEmitter;
  51   public:
  52     static char ID;
  53
  54     /// Return the ELFCodeEmitter as an instance of ObjectCodeEmitter
  55     ObjectCodeEmitter *getObjectCodeEmitter() {
  56       return reinterpret_cast<ObjectCodeEmitter*>(ElfCE);
  57     }
  58
  59     ELFWriter(raw_ostream &O, TargetMachine &TM);
  60     ~ELFWriter();
  61
  62   protected:
  63     /// Output stream to send the resultant object file to.
  64     raw_ostream &O;
  65
  66     /// Target machine description.
  67     TargetMachine &TM;
  68
  69     MCContext &OutContext;
  70
  71     /// Target Elf Writer description.
  72     const TargetELFWriterInfo *TEW;
  73
  74     /// Mang - The object used to perform name mangling for this module.
  75     Mangler *Mang;
  76
  77     /// MCE - The MachineCodeEmitter object that we are exposing to emit machine
  78     /// code for functions to the .o file.
  79     ELFCodeEmitter *ElfCE;
  80
  81     /// TAI - Target Asm Info, provide information about section names for
  82     /// globals and other target specific stuff.
  83     const TargetAsmInfo *TAI;
  84
  85     //===------------------------------------------------------------------===//
  86     // Properties inferred automatically from the target machine.
  87     //===------------------------------------------------------------------===//
  88
  89     /// is64Bit/isLittleEndian - This information is inferred from the target
  90     /// machine directly, indicating whether to emit a 32- or 64-bit ELF file.
  91     bool is64Bit, isLittleEndian;
  92
  93     /// doInitialization - Emit the file header and all of the global variables
  94     /// for the module to the ELF file.
  95     bool doInitialization(Module &M);
  96     bool runOnMachineFunction(MachineFunction &MF);
  97
  98     /// doFinalization - Now that the module has been completely processed, emit
  99     /// the ELF file to 'O'.
 100     bool doFinalization(Module &M);
 101
 102   private:
 103     /// Blob containing the Elf header
 104     BinaryObject ElfHdr;
 105
 106     /// SectionList - This is the list of sections that we have emitted to the
 107     /// file. Once the file has been completely built, the section header table
 108     /// is constructed from this info.
 109     std::vector<ELFSection*> SectionList;
 110     unsigned NumSections;   // Always = SectionList.size()
 111
 112     /// SectionLookup - This is a mapping from section name to section number in
 113     /// the SectionList. Used to quickly gather the Section Index from TAI names
 114     std::map<std::string, ELFSection*> SectionLookup;
 115
 116     /// PendingGlobals - Globals not processed as symbols yet.
 117     SetVector<const GlobalValue*> PendingGlobals;
 118
 119     /// GblSymLookup - This is a mapping from global value to a symbol index
 120     /// in the symbol table or private symbols list. This is useful since reloc
 121     /// symbol references must be quickly mapped to their indices on the lists.
 122     std::map<const GlobalValue*, uint32_t> GblSymLookup;
 123
 124     /// PendingExternals - Externals not processed as symbols yet.
 125     SetVector<const char *> PendingExternals;
 126
 127     /// ExtSymLookup - This is a mapping from externals to a symbol index
 128     /// in the symbol table list. This is useful since reloc symbol references
 129     /// must be quickly mapped to their symbol table indices.
 130     std::map<const char *, uint32_t> ExtSymLookup;
 131
 132     /// SymbolList - This is the list of symbols emitted to the symbol table.
 133     /// When the SymbolList is finally built, local symbols must be placed in
 134     /// the beginning while non-locals at the end.
 135     std::vector<ELFSym*> SymbolList;
 136
 137     /// PrivateSyms - Record private symbols, every symbol here must never be
 138     /// present in the SymbolList.
 139     std::vector<ELFSym*> PrivateSyms;
 140
 141     // Remove tab from section name prefix. This is necessary becase TAI
 142     // sometimes return a section name prefixed with elf unused chars. This is
 143     // a little bit dirty. FIXME: find a better approach, maybe add more
 144     // methods to TAI to get the clean name?
 145     void fixNameForSection(std::string &Name) {
 146       size_t Pos = Name.find("\t");
 147       if (Pos != std::string::npos)
 148         Name.erase(Pos, 1);
 149
 150       Pos = Name.find(".section ");
 151       if (Pos != std::string::npos)
 152         Name.erase(Pos, 9);
 153
 154       Pos = Name.find("\n");
 155       if (Pos != std::string::npos)
 156         Name.erase(Pos, 1);
 157     }
 158
 159     /// getSection - Return the section with the specified name, creating a new
 160     /// section if one does not already exist.
 161     ELFSection &getSection(const std::string &Name, unsigned Type,
 162                            unsigned Flags = 0, unsigned Align = 0) {
 163       std::string SName(Name);
 164       fixNameForSection(SName);
 165
 166       ELFSection *&SN = SectionLookup[SName];
 167       if (SN) return *SN;
 168
 169       SectionList.push_back(new ELFSection(SName, isLittleEndian, is64Bit));
 170       SN = SectionList.back();
 171       SN->SectionIdx = NumSections++;
 172       SN->Type = Type;
 173       SN->Flags = Flags;
 174       SN->Link = ELFSection::SHN_UNDEF;
 175       SN->Align = Align;
 176       return *SN;
 177     }
 178
 179     /// TODO: support mangled names here to emit the right .text section
 180     /// for c++ object files.
 181     ELFSection &getTextSection() {
 182       return getSection(".text", ELFSection::SHT_PROGBITS,
 183                         ELFSection::SHF_EXECINSTR | ELFSection::SHF_ALLOC);
 184     }
 185
 186     ELFSection &getNonExecStackSection() {
 187       return getSection(".note.GNU-stack", ELFSection::SHT_PROGBITS, 0, 1);
 188     }
 189
 190     ELFSection &getSymbolTableSection() {
 191       return getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
 192     }
 193
 194     ELFSection &getStringTableSection() {
 195       return getSection(".strtab", ELFSection::SHT_STRTAB, 0, 1);
 196     }
 197
 198     ELFSection &getSectionHeaderStringTableSection() {
 199       return getSection(".shstrtab", ELFSection::SHT_STRTAB, 0, 1);
 200     }
 201
 202     ELFSection &getDataSection() {
 203       return getSection(".data", ELFSection::SHT_PROGBITS,
 204                         ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC, 4);
 205     }
 206
 207     ELFSection &getBSSSection() {
 208       return getSection(".bss", ELFSection::SHT_NOBITS,
 209                         ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC, 4);
 210     }
 211
 212     ELFSection &getNullSection() {
 213       return getSection("", ELFSection::SHT_NULL, 0);
 214     }
 215
 216     ELFSection &getJumpTableSection();
 217     ELFSection &getConstantPoolSection(MachineConstantPoolEntry &CPE);
 218     ELFSection &getRelocSection(ELFSection &S);
 219
 220     // Helpers for obtaining ELF specific info.
 221     unsigned getGlobalELFBinding(const GlobalValue *GV);
 222     unsigned getGlobalELFType(const GlobalValue *GV);
 223     unsigned getGlobalELFVisibility(const GlobalValue *GV);
 224     unsigned getElfSectionFlags(SectionKind Kind);
 225
 226     // addGlobalSymbol - Add a global to be processed and to the
 227     // global symbol lookup, use a zero index for non private symbols
 228     // because the table index will be determined later.
 229     void addGlobalSymbol(const GlobalValue *GV);
 230
 231     // addExternalSymbol - Add the external to be processed and to the
 232     // external symbol lookup, use a zero index because the symbol
 233     // table index will be determined later
 234     void addExternalSymbol(const char *External);
 235
 236     // As we complete the ELF file, we need to update fields in the ELF header
 237     // (e.g. the location of the section table).  These members keep track of
 238     // the offset in ELFHeader of these various pieces to update and other
 239     // locations in the file.
 240     unsigned ELFHdr_e_shoff_Offset;     // e_shoff    in ELF header.
 241     unsigned ELFHdr_e_shstrndx_Offset;  // e_shstrndx in ELF header.
 242     unsigned ELFHdr_e_shnum_Offset;     // e_shnum    in ELF header.
 243
 244   private:
 245     void EmitGlobal(const GlobalValue *GV);
 246     void EmitGlobalConstant(const Constant *C, ELFSection &GblS);
 247     void EmitGlobalConstantStruct(const ConstantStruct *CVS,
 248                                   ELFSection &GblS);
 249     ELFSection &getGlobalSymELFSection(const GlobalVariable *GV, ELFSym &Sym);
 250     void EmitRelocations();
 251     void EmitRelocation(BinaryObject &RelSec, ELFRelocation &Rel, bool HasRelA);
 252     void EmitSectionHeader(BinaryObject &SHdrTab, const ELFSection &SHdr);
 253     void EmitSectionTableStringTable();
 254     void EmitSymbol(BinaryObject &SymbolTable, ELFSym &Sym);
 255     void EmitSymbolTable();
 256     void EmitStringTable(const std::string &ModuleName);
 257     void OutputSectionsAndSectionTable();
 258     void RelocateField(BinaryObject &BO, uint32_t Offset, int64_t Value,
 259                        unsigned Size);
 260     unsigned SortSymbols();
 261   };
 262 }
 263
 264 #endif