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/CodeGen/MachineFunctionPass.h"
  18 #include <list>
  19 #include <map>
  20
  21 namespace llvm {
  22   class GlobalVariable;
  23   class Mangler;
  24   class MachineCodeEmitter;
  25   class ELFCodeEmitter;
  26   class raw_ostream;
  27
  28   /// ELFWriter - This class implements the common target-independent code for
  29   /// writing ELF files.  Targets should derive a class from this to
  30   /// parameterize the output format.
  31   ///
  32   class ELFWriter : public MachineFunctionPass {
  33     friend class ELFCodeEmitter;
  34   public:
  35     static char ID;
  36
  37     MachineCodeEmitter &getMachineCodeEmitter() const {
  38       return *(MachineCodeEmitter*)MCE;
  39     }
  40
  41     ELFWriter(raw_ostream &O, TargetMachine &TM);
  42     ~ELFWriter();
  43
  44     typedef std::vector<unsigned char> DataBuffer;
  45
  46   protected:
  47     /// Output stream to send the resultant object file to.
  48     ///
  49     raw_ostream &O;
  50
  51     /// Target machine description.
  52     ///
  53     TargetMachine &TM;
  54
  55     /// Mang - The object used to perform name mangling for this module.
  56     ///
  57     Mangler *Mang;
  58
  59     /// MCE - The MachineCodeEmitter object that we are exposing to emit machine
  60     /// code for functions to the .o file.
  61     ELFCodeEmitter *MCE;
  62
  63     //===------------------------------------------------------------------===//
  64     // Properties to be set by the derived class ctor, used to configure the
  65     // ELFWriter.
  66
  67     // e_machine - This field is the target specific value to emit as the
  68     // e_machine member of the ELF header.
  69     unsigned short e_machine;
  70
  71     // e_flags - The machine flags for the target.  This defaults to zero.
  72     unsigned e_flags;
  73
  74     //===------------------------------------------------------------------===//
  75     // Properties inferred automatically from the target machine.
  76     //
  77
  78     /// is64Bit/isLittleEndian - This information is inferred from the target
  79     /// machine directly, indicating whether to emit a 32- or 64-bit ELF file.
  80     bool is64Bit, isLittleEndian;
  81
  82     /// doInitialization - Emit the file header and all of the global variables
  83     /// for the module to the ELF file.
  84     bool doInitialization(Module &M);
  85
  86     bool runOnMachineFunction(MachineFunction &MF);
  87
  88
  89     /// doFinalization - Now that the module has been completely processed, emit
  90     /// the ELF file to 'O'.
  91     bool doFinalization(Module &M);
  92
  93   private:
  94     // The buffer we accumulate the file header into.  Note that this should be
  95     // changed into something much more efficient later (and the bitcode writer
  96     // as well!).
  97     DataBuffer FileHeader;
  98
  99     /// ELFSection - This struct contains information about each section that is
 100     /// emitted to the file.  This is eventually turned into the section header
 101     /// table at the end of the file.
 102     struct ELFSection {
 103       std::string Name;       // Name of the section.
 104       unsigned NameIdx;       // Index in .shstrtab of name, once emitted.
 105       unsigned Type;
 106       unsigned Flags;
 107       uint64_t Addr;
 108       unsigned Offset;
 109       unsigned Size;
 110       unsigned Link;
 111       unsigned Info;
 112       unsigned Align;
 113       unsigned EntSize;
 114
 115       /// SectionIdx - The number of the section in the Section Table.
 116       ///
 117       unsigned short SectionIdx;
 118
 119       /// SectionData - The actual data for this section which we are building
 120       /// up for emission to the file.
 121       DataBuffer SectionData;
 122
 123       enum { SHT_NULL = 0, SHT_PROGBITS = 1, SHT_SYMTAB = 2, SHT_STRTAB = 3,
 124              SHT_RELA = 4, SHT_HASH = 5, SHT_DYNAMIC = 6, SHT_NOTE = 7,
 125              SHT_NOBITS = 8, SHT_REL = 9, SHT_SHLIB = 10, SHT_DYNSYM = 11 };
 126       enum { SHN_UNDEF = 0, SHN_ABS = 0xFFF1, SHN_COMMON = 0xFFF2 };
 127       enum {   // SHF - ELF Section Header Flags
 128         SHF_WRITE            = 1 << 0, // Writable
 129         SHF_ALLOC            = 1 << 1, // Mapped into the process addr space
 130         SHF_EXECINSTR        = 1 << 2, // Executable
 131         SHF_MERGE            = 1 << 4, // Might be merged if equal
 132         SHF_STRINGS          = 1 << 5, // Contains null-terminated strings
 133         SHF_INFO_LINK        = 1 << 6, // 'sh_info' contains SHT index
 134         SHF_LINK_ORDER       = 1 << 7, // Preserve order after combining
 135         SHF_OS_NONCONFORMING = 1 << 8, // nonstandard OS support required
 136         SHF_GROUP            = 1 << 9, // Section is a member of a group
 137         SHF_TLS              = 1 << 10 // Section holds thread-local data
 138       };
 139
 140       ELFSection(const std::string &name)
 141         : Name(name), Type(0), Flags(0), Addr(0), Offset(0), Size(0),
 142           Link(0), Info(0), Align(0), EntSize(0) {
 143       }
 144     };
 145
 146     /// SectionList - This is the list of sections that we have emitted to the
 147     /// file.  Once the file has been completely built, the section header table
 148     /// is constructed from this info.
 149     std::list<ELFSection> SectionList;
 150     unsigned NumSections;   // Always = SectionList.size()
 151
 152     /// SectionLookup - This is a mapping from section name to section number in
 153     /// the SectionList.
 154     std::map<std::string, ELFSection*> SectionLookup;
 155
 156     /// getSection - Return the section with the specified name, creating a new
 157     /// section if one does not already exist.
 158     ELFSection &getSection(const std::string &Name,
 159                            unsigned Type, unsigned Flags = 0) {
 160       ELFSection *&SN = SectionLookup[Name];
 161       if (SN) return *SN;
 162
 163       SectionList.push_back(Name);
 164       SN = &SectionList.back();
 165       SN->SectionIdx = NumSections++;
 166       SN->Type = Type;
 167       SN->Flags = Flags;
 168       return *SN;
 169     }
 170
 171     ELFSection &getDataSection() {
 172       return getSection(".data", ELFSection::SHT_PROGBITS,
 173                         ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC);
 174     }
 175     ELFSection &getBSSSection() {
 176       return getSection(".bss", ELFSection::SHT_NOBITS,
 177                         ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC);
 178     }
 179
 180     /// ELFSym - This struct contains information about each symbol that is
 181     /// added to logical symbol table for the module.  This is eventually
 182     /// turned into a real symbol table in the file.
 183     struct ELFSym {
 184       const GlobalValue *GV;    // The global value this corresponds to.
 185       unsigned NameIdx;         // Index in .strtab of name, once emitted.
 186       uint64_t Value;
 187       unsigned Size;
 188       unsigned char Info;
 189       unsigned char Other;
 190       unsigned short SectionIdx;
 191
 192       enum { STB_LOCAL = 0, STB_GLOBAL = 1, STB_WEAK = 2 };
 193       enum { STT_NOTYPE = 0, STT_OBJECT = 1, STT_FUNC = 2, STT_SECTION = 3,
 194              STT_FILE = 4 };
 195       ELFSym(const GlobalValue *gv) : GV(gv), Value(0), Size(0), Info(0),
 196                                       Other(0), SectionIdx(0) {}
 197
 198       void SetBind(unsigned X) {
 199         assert(X == (X & 0xF) && "Bind value out of range!");
 200         Info = (Info & 0x0F) | (X << 4);
 201       }
 202       void SetType(unsigned X) {
 203         assert(X == (X & 0xF) && "Type value out of range!");
 204         Info = (Info & 0xF0) | X;
 205       }
 206     };
 207
 208     /// SymbolTable - This is the list of symbols we have emitted to the file.
 209     /// This actually gets rearranged before emission to the file (to put the
 210     /// local symbols first in the list).
 211     std::vector<ELFSym> SymbolTable;
 212
 213     // As we complete the ELF file, we need to update fields in the ELF header
 214     // (e.g. the location of the section table).  These members keep track of
 215     // the offset in ELFHeader of these various pieces to update and other
 216     // locations in the file.
 217     unsigned ELFHeader_e_shoff_Offset;     // e_shoff    in ELF header.
 218     unsigned ELFHeader_e_shstrndx_Offset;  // e_shstrndx in ELF header.
 219     unsigned ELFHeader_e_shnum_Offset;     // e_shnum    in ELF header.
 220   private:
 221     void EmitGlobal(GlobalVariable *GV);
 222
 223     void EmitSymbolTable();
 224
 225     void EmitSectionTableStringTable();
 226     void OutputSectionsAndSectionTable();
 227   };
 228 }
 229
 230 #endif