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 TargetLoweringObjectFile;
  37   class raw_ostream;
  38   class SectionKind;
  39   class MCContext;
  40
  41   typedef std::vector<ELFSym*>::iterator ELFSymIter;
  42   typedef std::vector<ELFSection*>::iterator ELFSectionIter;
  43   typedef SetVector<const GlobalValue*>::const_iterator PendingGblsIter;
  44   typedef SetVector<const char *>::const_iterator PendingExtsIter;
  45
  46   /// ELFWriter - This class implements the common target-independent code for
  47   /// writing ELF files.  Targets should derive a class from this to
  48   /// parameterize the output format.
  49   ///
  50   class ELFWriter : public MachineFunctionPass {
  51     friend class ELFCodeEmitter;
  52   public:
  53     static char ID;
  54
  55     /// Return the ELFCodeEmitter as an instance of ObjectCodeEmitter
  56     ObjectCodeEmitter *getObjectCodeEmitter() {
  57       return reinterpret_cast<ObjectCodeEmitter*>(ElfCE);
  58     }
  59
  60     ELFWriter(raw_ostream &O, TargetMachine &TM);
  61     ~ELFWriter();
  62
  63   protected:
  64     /// Output stream to send the resultant object file to.
  65     raw_ostream &O;
  66
  67     /// Target machine description.
  68     TargetMachine &TM;
  69
  70     /// Context object for machine code objects.
  71     MCContext &OutContext;
  72
  73     /// Target Elf Writer description.
  74     const TargetELFWriterInfo *TEW;
  75
  76     /// Mang - The object used to perform name mangling for this module.
  77     Mangler *Mang;
  78
  79     /// MCE - The MachineCodeEmitter object that we are exposing to emit machine
  80     /// code for functions to the .o file.
  81     ELFCodeEmitter *ElfCE;
  82
  83     /// TLOF - Target Lowering Object File, provide section names for globals
  84     /// and other object file specific stuff
  85     const TargetLoweringObjectFile &TLOF;
  86
  87     /// TAI - Target Asm Info, provide information about section names for
  88     /// globals and other target specific stuff.
  89     const TargetAsmInfo *TAI;
  90
  91     //===------------------------------------------------------------------===//
  92     // Properties inferred automatically from the target machine.
  93     //===------------------------------------------------------------------===//
  94
  95     /// is64Bit/isLittleEndian - This information is inferred from the target
  96     /// machine directly, indicating whether to emit a 32- or 64-bit ELF file.
  97     bool is64Bit, isLittleEndian;
  98
  99     /// doInitialization - Emit the file header and all of the global variables
 100     /// for the module to the ELF file.
 101     bool doInitialization(Module &M);
 102     bool runOnMachineFunction(MachineFunction &MF);
 103
 104     /// doFinalization - Now that the module has been completely processed, emit
 105     /// the ELF file to 'O'.
 106     bool doFinalization(Module &M);
 107
 108   private:
 109     /// Blob containing the Elf header
 110     BinaryObject ElfHdr;
 111
 112     /// SectionList - This is the list of sections that we have emitted to the
 113     /// file. Once the file has been completely built, the section header table
 114     /// is constructed from this info.
 115     std::vector<ELFSection*> SectionList;
 116     unsigned NumSections;   // Always = SectionList.size()
 117
 118     /// SectionLookup - This is a mapping from section name to section number in
 119     /// the SectionList. Used to quickly gather the Section Index from TAI names
 120     std::map<std::string, ELFSection*> SectionLookup;
 121
 122     /// PendingGlobals - Globals not processed as symbols yet.
 123     SetVector<const GlobalValue*> PendingGlobals;
 124
 125     /// GblSymLookup - This is a mapping from global value to a symbol index
 126     /// in the symbol table or private symbols list. This is useful since reloc
 127     /// symbol references must be quickly mapped to their indices on the lists.
 128     std::map<const GlobalValue*, uint32_t> GblSymLookup;
 129
 130     /// PendingExternals - Externals not processed as symbols yet.
 131     SetVector<const char *> PendingExternals;
 132
 133     /// ExtSymLookup - This is a mapping from externals to a symbol index
 134     /// in the symbol table list. This is useful since reloc symbol references
 135     /// must be quickly mapped to their symbol table indices.
 136     std::map<const char *, uint32_t> ExtSymLookup;
 137
 138     /// SymbolList - This is the list of symbols emitted to the symbol table.
 139     /// When the SymbolList is finally built, local symbols must be placed in
 140     /// the beginning while non-locals at the end.
 141     std::vector<ELFSym*> SymbolList;
 142
 143     /// PrivateSyms - Record private symbols, every symbol here must never be
 144     /// present in the SymbolList.
 145     std::vector<ELFSym*> PrivateSyms;
 146
 147     // Remove tab from section name prefix. This is necessary becase TAI
 148     // sometimes return a section name prefixed with elf unused chars. This is
 149     // a little bit dirty. FIXME: find a better approach, maybe add more
 150     // methods to TAI to get the clean name?
 151     void fixNameForSection(std::string &Name) {
 152       size_t Pos = Name.find("\t");
 153       if (Pos != std::string::npos)
 154         Name.erase(Pos, 1);
 155
 156       Pos = Name.find(".section ");
 157       if (Pos != std::string::npos)
 158         Name.erase(Pos, 9);
 159
 160       Pos = Name.find("\n");
 161       if (Pos != std::string::npos)
 162         Name.erase(Pos, 1);
 163     }
 164
 165     /// getSection - Return the section with the specified name, creating a new
 166     /// section if one does not already exist.
 167     ELFSection &getSection(const std::string &Name, unsigned Type,
 168                            unsigned Flags = 0, unsigned Align = 0) {
 169       std::string SName(Name);
 170       fixNameForSection(SName);
 171
 172       ELFSection *&SN = SectionLookup[SName];
 173       if (SN) return *SN;
 174
 175       SectionList.push_back(new ELFSection(SName, isLittleEndian, is64Bit));
 176       SN = SectionList.back();
 177       SN->SectionIdx = NumSections++;
 178       SN->Type = Type;
 179       SN->Flags = Flags;
 180       SN->Link = ELFSection::SHN_UNDEF;
 181       SN->Align = Align;
 182       return *SN;
 183     }
 184
 185     ELFSection &getNonExecStackSection() {
 186       return getSection(".note.GNU-stack", ELFSection::SHT_PROGBITS, 0, 1);
 187     }
 188
 189     ELFSection &getSymbolTableSection() {
 190       return getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
 191     }
 192
 193     ELFSection &getStringTableSection() {
 194       return getSection(".strtab", ELFSection::SHT_STRTAB, 0, 1);
 195     }
 196
 197     ELFSection &getSectionHeaderStringTableSection() {
 198       return getSection(".shstrtab", ELFSection::SHT_STRTAB, 0, 1);
 199     }
 200
 201     ELFSection &getDataSection() {
 202       return getSection(".data", ELFSection::SHT_PROGBITS,
 203                         ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC, 4);
 204     }
 205
 206     ELFSection &getBSSSection() {
 207       return getSection(".bss", ELFSection::SHT_NOBITS,
 208                         ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC, 4);
 209     }
 210
 211     ELFSection &getNullSection() {
 212       return getSection("", ELFSection::SHT_NULL, 0);
 213     }
 214
 215     ELFSection &getCtorSection();
 216     ELFSection &getDtorSection();
 217     ELFSection &getJumpTableSection();
 218     ELFSection &getConstantPoolSection(MachineConstantPoolEntry &CPE);
 219     ELFSection &getTextSection(Function *F);
 220     ELFSection &getRelocSection(ELFSection &S);
 221
 222     // Helpers for obtaining ELF specific info.
 223     unsigned getGlobalELFBinding(const GlobalValue *GV);
 224     unsigned getGlobalELFType(const GlobalValue *GV);
 225     unsigned getGlobalELFVisibility(const GlobalValue *GV);
 226     unsigned getElfSectionFlags(SectionKind Kind, bool IsAlloc = true);
 227
 228     // addGlobalSymbol - Add a global to be processed and to
 229     // the global symbol lookup, use a zero index because the table
 230     // index will be determined later.
 231     void addGlobalSymbol(const GlobalValue *GV, bool AddToLookup = false);
 232
 233     // addExternalSymbol - Add the external to be processed and to the
 234     // external symbol lookup, use a zero index because the symbol
 235     // table index will be determined later
 236     void addExternalSymbol(const char *External);
 237
 238     // As we complete the ELF file, we need to update fields in the ELF header
 239     // (e.g. the location of the section table).  These members keep track of
 240     // the offset in ELFHeader of these various pieces to update and other
 241     // locations in the file.
 242     unsigned ELFHdr_e_shoff_Offset;     // e_shoff    in ELF header.
 243     unsigned ELFHdr_e_shstrndx_Offset;  // e_shstrndx in ELF header.
 244     unsigned ELFHdr_e_shnum_Offset;     // e_shnum    in ELF header.
 245
 246   private:
 247     void EmitGlobal(const GlobalValue *GV);
 248     void EmitGlobalConstant(const Constant *C, ELFSection &GblS);
 249     void EmitGlobalConstantStruct(const ConstantStruct *CVS,
 250                                   ELFSection &GblS);
 251     void emitGlobalDataRelocation(const GlobalValue *GV, unsigned Size,
 252                                   ELFSection &GblS);
 253     bool EmitSpecialLLVMGlobal(const GlobalVariable *GV);
 254     void EmitXXStructorList(Constant *List, ELFSection &Xtor);
 255     void EmitRelocations();
 256     void EmitRelocation(BinaryObject &RelSec, ELFRelocation &Rel, bool HasRelA);
 257     void EmitSectionHeader(BinaryObject &SHdrTab, const ELFSection &SHdr);
 258     void EmitSectionTableStringTable();
 259     void EmitSymbol(BinaryObject &SymbolTable, ELFSym &Sym);
 260     void EmitSymbolTable();
 261     void EmitStringTable(const std::string &ModuleName);
 262     void OutputSectionsAndSectionTable();
 263     void RelocateField(BinaryObject &BO, uint32_t Offset, int64_t Value,
 264                        unsigned Size);
 265     unsigned SortSymbols();
 266   };
 267 }
 268
 269 #endif