lib/CodeGen/MachOWriter.cpp

//===-- MachOWriter.cpp - Target-independent Mach-O Writer code -----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Nate Begeman and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the target-independent Mach-O writer.  This file writes
// out the Mach-O file in the following order:
//
//  #1 FatHeader (universal-only)
//  #2 FatArch (universal-only, 1 per universal arch)
//  Per arch:
//    #3 Header
//    #4 Load Commands
//    #5 Sections
//    #6 Relocations
//    #7 Symbols
//    #8 Strings
//
//===----------------------------------------------------------------------===//

#include "llvm/Module.h"
#include "llvm/CodeGen/MachineCodeEmitter.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachOWriter.h"
#include "llvm/ExecutionEngine/ExecutionEngine.h"
#include "llvm/Target/TargetJITInfo.h"
#include "llvm/Support/Mangler.h"
#include "llvm/Support/MathExtras.h"
#include <algorithm>
#include <iostream>
using namespace llvm;

//===----------------------------------------------------------------------===//
//                       MachOCodeEmitter Implementation
//===----------------------------------------------------------------------===//

namespace llvm {
  /// MachOCodeEmitter - This class is used by the MachOWriter to emit the code 
  /// for functions to the Mach-O file.
  class MachOCodeEmitter : public MachineCodeEmitter {
    MachOWriter &MOW;
    
    /// MOS - The current section we're writing to
    MachOWriter::MachOSection *MOS;

    /// Relocations - These are the relocations that the function needs, as
    /// emitted.
    std::vector<MachineRelocation> Relocations;

    /// MBBLocations - This vector is a mapping from MBB ID's to their address.
    /// It is filled in by the StartMachineBasicBlock callback and queried by
    /// the getMachineBasicBlockAddress callback.
    std::vector<intptr_t> MBBLocations;
    
  public:
    MachOCodeEmitter(MachOWriter &mow) : MOW(mow) {}

    void startFunction(MachineFunction &F);
    bool finishFunction(MachineFunction &F);

    void addRelocation(const MachineRelocation &MR) {
      Relocations.push_back(MR);
    }
    
    virtual void StartMachineBasicBlock(MachineBasicBlock *MBB) {
      if (MBBLocations.size() <= (unsigned)MBB->getNumber())
        MBBLocations.resize((MBB->getNumber()+1)*2);
      MBBLocations[MBB->getNumber()] = getCurrentPCValue();
    }

    virtual intptr_t getConstantPoolEntryAddress(unsigned Index) const {
      assert(0 && "CP not implementated yet!");
      return 0;
    }
    virtual intptr_t getJumpTableEntryAddress(unsigned Index) const {
      assert(0 && "JT not implementated yet!");
      return 0;
    }

    virtual intptr_t getMachineBasicBlockAddress(MachineBasicBlock *MBB) const {
      assert(MBBLocations.size() > (unsigned)MBB->getNumber() && 
             MBBLocations[MBB->getNumber()] && "MBB not emitted!");
      return MBBLocations[MBB->getNumber()];
    }

    /// JIT SPECIFIC FUNCTIONS - DO NOT IMPLEMENT THESE HERE!
    void startFunctionStub(unsigned StubSize) {
      assert(0 && "JIT specific function called!");
      abort();
    }
    void *finishFunctionStub(const Function *F) {
      assert(0 && "JIT specific function called!");
      abort();
      return 0;
    }
  };
}

/// startFunction - This callback is invoked when a new machine function is
/// about to be emitted.
void MachOCodeEmitter::startFunction(MachineFunction &F) {
  // Align the output buffer to the appropriate alignment, power of 2.
  // FIXME: GENERICIZE!!
  unsigned Align = 4;

  // Get the Mach-O Section that this function belongs in.
  MOS = &MOW.getTextSection();
  
   // FIXME: better memory management
  MOS->SectionData.reserve(4096);
  BufferBegin = &(MOS->SectionData[0]);
  BufferEnd = BufferBegin + MOS->SectionData.capacity();
  CurBufferPtr = BufferBegin + MOS->size;

  // Upgrade the section alignment if required.
  if (MOS->align < Align) MOS->align = Align;

  // Make sure we only relocate to this function's MBBs.
  MBBLocations.clear();
}

/// finishFunction - This callback is invoked after the function is completely
/// finished.
bool MachOCodeEmitter::finishFunction(MachineFunction &F) {
  MOS->size += CurBufferPtr - BufferBegin;
  
  // Get a symbol for the function to add to the symbol table
  const GlobalValue *FuncV = F.getFunction();
  MachOSym FnSym(FuncV, MOW.Mang->getValueName(FuncV), MOS->Index);

  // FIXME: emit constant pool to appropriate section(s)
  // FIXME: emit jump table to appropriate section
  
  // Resolve the function's relocations either to concrete pointers in the case
  // of branches from one block to another, or to target relocation entries.
  for (unsigned i = 0, e = Relocations.size(); i != e; ++i) {
    MachineRelocation &MR = Relocations[i];
    if (MR.isBasicBlock()) {
      void *MBBAddr = (void *)getMachineBasicBlockAddress(MR.getBasicBlock());
      MR.setResultPointer(MBBAddr);
      MOW.TM.getJITInfo()->relocate(BufferBegin, &MR, 1, 0);
    } else if (MR.isConstantPoolIndex() || MR.isJumpTableIndex()) {
      // Get the address of the index.
      uint64_t Addr = 0;
      // Generate the relocation(s) for the index.
      MOW.GetTargetRelocation(*MOS, MR, Addr);
    } else {
      // Handle other types later once we've finalized the sections in the file.
      MOS->Relocations.push_back(MR);
    }
  }
  Relocations.clear();
  
  // Finally, add it to the symtab.
  MOW.SymbolTable.push_back(FnSym);
  return false;
}

//===----------------------------------------------------------------------===//
//                          MachOWriter Implementation
//===----------------------------------------------------------------------===//

MachOWriter::MachOWriter(std::ostream &o, TargetMachine &tm) : O(o), TM(tm) {
  is64Bit = TM.getTargetData()->getPointerSizeInBits() == 64;
  isLittleEndian = TM.getTargetData()->isLittleEndian();

  // Create the machine code emitter object for this target.
  MCE = new MachOCodeEmitter(*this);
}

MachOWriter::~MachOWriter() {
  delete MCE;
}

void MachOWriter::AddSymbolToSection(MachOSection &Sec, GlobalVariable *GV) {
  const Type *Ty = GV->getType()->getElementType();
  unsigned Size = TM.getTargetData()->getTypeSize(Ty);
  unsigned Align = Log2_32(TM.getTargetData()->getTypeAlignment(Ty));
  
  MachOSym Sym(GV, Mang->getValueName(GV), Sec.Index);
  // Reserve space in the .bss section for this symbol while maintaining the
  // desired section alignment, which must be at least as much as required by
  // this symbol.
  if (Align) {
    Sec.align = std::max(unsigned(Sec.align), Align);
    Sec.size = (Sec.size + Align - 1) & ~(Align-1);
  }
  // Record the offset of the symbol, and then allocate space for it.
  Sym.n_value = Sec.size;
  Sec.size += Size;

  switch (GV->getLinkage()) {
  default:  // weak/linkonce handled above
    assert(0 && "Unexpected linkage type!");
  case GlobalValue::ExternalLinkage:
    Sym.n_type |= MachOSym::N_EXT;
    break;
  case GlobalValue::InternalLinkage:
    break;
  }
  SymbolTable.push_back(Sym);
}

void MachOWriter::EmitGlobal(GlobalVariable *GV) {
  const Type *Ty = GV->getType()->getElementType();
  unsigned Size = TM.getTargetData()->getTypeSize(Ty);
  bool NoInit = !GV->hasInitializer();
  
  // If this global has a zero initializer, it is part of the .bss or common
  // section.
  if (NoInit || GV->getInitializer()->isNullValue()) {
    // If this global is part of the common block, add it now.  Variables are
    // part of the common block if they are zero initialized and allowed to be
    // merged with other symbols.
    if (NoInit || GV->hasLinkOnceLinkage() || GV->hasWeakLinkage()) {
      MachOSym ExtOrCommonSym(GV, Mang->getValueName(GV), MachOSym::NO_SECT);
      // For undefined (N_UNDF) external (N_EXT) types, n_value is the size in
      // bytes of the symbol.
      ExtOrCommonSym.n_value = Size;
      // If the symbol is external, we'll put it on a list of symbols whose
      // addition to the symbol table is being pended until we find a reference
      if (NoInit)
        PendingSyms.push_back(ExtOrCommonSym);
      else
        SymbolTable.push_back(ExtOrCommonSym);
      return;
    }
    // Otherwise, this symbol is part of the .bss section.
    MachOSection &BSS = getBSSSection();
    AddSymbolToSection(BSS, GV);
    return;
  }
  
  // Scalar read-only data goes in a literal section if the scalar is 4, 8, or
  // 16 bytes, or a cstring.  Other read only data goes into a regular const
  // section.  Read-write data goes in the data section.
  MachOSection &Sec = GV->isConstant() ? getConstSection(Ty) : getDataSection();
  AddSymbolToSection(Sec, GV);
  
  // FIXME: A couple significant changes are required for this to work, even for
  //        trivial cases such as a constant integer:
  //   0. InitializeMemory needs to be split out of ExecutionEngine.  We don't
  //      want to have to create an ExecutionEngine such as JIT just to write
  //      some bytes into a buffer.  The only thing necessary for
  //      InitializeMemory to function properly should be TargetData.
  //
  //   1. InitializeMemory needs to be enhanced to return MachineRelocations 
  //      rather than accessing the address of objects such basic blocks, 
  //      constant pools, and jump tables.  The client of InitializeMemory such
  //      as an object writer or jit emitter should then handle these relocs
  //      appropriately.
  //
  // FIXME: need to allocate memory for the global initializer.
}


bool MachOWriter::runOnMachineFunction(MachineFunction &MF) {
  // Nothing to do here, this is all done through the MCE object.
  return false;
}

bool MachOWriter::doInitialization(Module &M) {
  // Set the magic value, now that we know the pointer size and endianness
  Header.setMagic(isLittleEndian, is64Bit);

  // Set the file type
  // FIXME: this only works for object files, we do not support the creation
  //        of dynamic libraries or executables at this time.
  Header.filetype = MachOHeader::MH_OBJECT;

  Mang = new Mangler(M);
  return false;
}

/// doFinalization - Now that the module has been completely processed, emit
/// the Mach-O file to 'O'.
bool MachOWriter::doFinalization(Module &M) {
  // FIXME: we don't handle debug info yet, we should probably do that.

  // Okay, the.text section has been completed, build the .data, .bss, and 
  // "common" sections next.
  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
       I != E; ++I)
    EmitGlobal(I);
  
  // Emit the symbol table to temporary buffers, so that we know the size of
  // the string table when we write the load commands in the next phase.
  BufferSymbolAndStringTable();
  
  // Emit the header and load commands.
  EmitHeaderAndLoadCommands();

  // Emit the text and data sections.
  EmitSections();

  // Emit the relocation entry data for each section.
  O.write((char*)&RelocBuffer[0], RelocBuffer.size());

  // Write the symbol table and the string table to the end of the file.
  O.write((char*)&SymT[0], SymT.size());
  O.write((char*)&StrT[0], StrT.size());

  // We are done with the abstract symbols.
  SectionList.clear();
  SymbolTable.clear();
  DynamicSymbolTable.clear();

  // Release the name mangler object.
  delete Mang; Mang = 0;
  return false;
}

void MachOWriter::EmitHeaderAndLoadCommands() {
  // Step #0: Fill in the segment load command size, since we need it to figure
  //          out the rest of the header fields
  MachOSegment SEG("", is64Bit);
  SEG.nsects  = SectionList.size();
  SEG.cmdsize = SEG.cmdSize(is64Bit) + 
                SEG.nsects * SectionList.begin()->cmdSize(is64Bit);
  
  // Step #1: calculate the number of load commands.  We always have at least
  //          one, for the LC_SEGMENT load command, plus two for the normal
  //          and dynamic symbol tables, if there are any symbols.
  Header.ncmds = SymbolTable.empty() ? 1 : 3;
  
  // Step #2: calculate the size of the load commands
  Header.sizeofcmds = SEG.cmdsize;
  if (!SymbolTable.empty())
    Header.sizeofcmds += SymTab.cmdsize + DySymTab.cmdsize;
    
  // Step #3: write the header to the file
  // Local alias to shortenify coming code.
  DataBuffer &FH = Header.HeaderData;
  outword(FH, Header.magic);
  outword(FH, Header.cputype);
  outword(FH, Header.cpusubtype);
  outword(FH, Header.filetype);
  outword(FH, Header.ncmds);
  outword(FH, Header.sizeofcmds);
  outword(FH, Header.flags);
  if (is64Bit)
    outword(FH, Header.reserved);
  
  // Step #4: Finish filling in the segment load command and write it out
  for (std::list<MachOSection>::iterator I = SectionList.begin(),
         E = SectionList.end(); I != E; ++I)
    SEG.filesize += I->size;
  SEG.vmsize = SEG.filesize;
  SEG.fileoff = Header.cmdSize(is64Bit) + Header.sizeofcmds;
  
  outword(FH, SEG.cmd);
  outword(FH, SEG.cmdsize);
  outstring(FH, SEG.segname, 16);
  outaddr(FH, SEG.vmaddr);
  outaddr(FH, SEG.vmsize);
  outaddr(FH, SEG.fileoff);
  outaddr(FH, SEG.filesize);
  outword(FH, SEG.maxprot);
  outword(FH, SEG.initprot);
  outword(FH, SEG.nsects);
  outword(FH, SEG.flags);
  
  // Step #5: Finish filling in the fields of the MachOSections 
  uint64_t currentAddr = 0;
  for (std::list<MachOSection>::iterator I = SectionList.begin(),
         E = SectionList.end(); I != E; ++I) {
    I->addr = currentAddr;
    I->offset = currentAddr + SEG.fileoff;
    // FIXME: do we need to do something with alignment here?
    currentAddr += I->size;
  }
  
  // Step #6: Calculate the number of relocations for each section and write out
  // the section commands for each section
  currentAddr += SEG.fileoff;
  for (std::list<MachOSection>::iterator I = SectionList.begin(),
         E = SectionList.end(); I != E; ++I) {
    // calculate the relocation info for this section command
    // FIXME: this could get complicated calculating the address argument, we 
    // should probably split this out into its own function.
    for (unsigned i = 0, e = I->Relocations.size(); i != e; ++i)
      GetTargetRelocation(*I, I->Relocations[i], 0);
    if (I->nreloc != 0) {
      I->reloff = currentAddr;
      currentAddr += I->nreloc * 8;
    }
    
    // write the finalized section command to the output buffer
    outstring(FH, I->sectname, 16);
    outstring(FH, I->segname, 16);
    outaddr(FH, I->addr);
    outaddr(FH, I->size);
    outword(FH, I->offset);
    outword(FH, I->align);
    outword(FH, I->reloff);
    outword(FH, I->nreloc);
    outword(FH, I->flags);
    outword(FH, I->reserved1);
    outword(FH, I->reserved2);
    if (is64Bit)
      outword(FH, I->reserved3);
  }
  
  // Step #7: Emit LC_SYMTAB/LC_DYSYMTAB load commands
  // FIXME: add size of relocs
  SymTab.symoff  = currentAddr;
  SymTab.nsyms   = SymbolTable.size();
  SymTab.stroff  = SymTab.symoff + SymT.size();
  SymTab.strsize = StrT.size();
  outword(FH, SymTab.cmd);
  outword(FH, SymTab.cmdsize);
  outword(FH, SymTab.symoff);
  outword(FH, SymTab.nsyms);
  outword(FH, SymTab.stroff);
  outword(FH, SymTab.strsize);

  // FIXME: set DySymTab fields appropriately
  // We should probably just update these in BufferSymbolAndStringTable since
  // thats where we're partitioning up the different kinds of symbols.
  outword(FH, DySymTab.cmd);
  outword(FH, DySymTab.cmdsize);
  outword(FH, DySymTab.ilocalsym);
  outword(FH, DySymTab.nlocalsym);
  outword(FH, DySymTab.iextdefsym);
  outword(FH, DySymTab.nextdefsym);
  outword(FH, DySymTab.iundefsym);
  outword(FH, DySymTab.nundefsym);
  outword(FH, DySymTab.tocoff);
  outword(FH, DySymTab.ntoc);
  outword(FH, DySymTab.modtaboff);
  outword(FH, DySymTab.nmodtab);
  outword(FH, DySymTab.extrefsymoff);
  outword(FH, DySymTab.nextrefsyms);
  outword(FH, DySymTab.indirectsymoff);
  outword(FH, DySymTab.nindirectsyms);
  outword(FH, DySymTab.extreloff);
  outword(FH, DySymTab.nextrel);
  outword(FH, DySymTab.locreloff);
  outword(FH, DySymTab.nlocrel);
  
  O.write((char*)&FH[0], FH.size());
}

/// EmitSections - Now that we have constructed the file header and load
/// commands, emit the data for each section to the file.
void MachOWriter::EmitSections() {
  for (std::list<MachOSection>::iterator I = SectionList.begin(),
         E = SectionList.end(); I != E; ++I) {
    O.write((char*)&I->SectionData[0], I->size);
  }
}

/// PartitionByLocal - Simple boolean predicate that returns true if Sym is
/// a local symbol rather than an external symbol.
bool MachOWriter::PartitionByLocal(const MachOSym &Sym) {
  // FIXME: Not totally sure if private extern counts as external
  return (Sym.n_type & (MachOSym::N_EXT | MachOSym::N_PEXT)) == 0;
}

/// PartitionByDefined - Simple boolean predicate that returns true if Sym is
/// defined in this module.
bool MachOWriter::PartitionByDefined(const MachOSym &Sym) {
  // FIXME: Do N_ABS or N_INDR count as defined?
  return (Sym.n_type & MachOSym::N_SECT) == MachOSym::N_SECT;
}

/// BufferSymbolAndStringTable - Sort the symbols we encountered and assign them
/// each a string table index so that they appear in the correct order in the
/// output file.
void MachOWriter::BufferSymbolAndStringTable() {
  // The order of the symbol table is:
  // 1. local symbols
  // 2. defined external symbols (sorted by name)
  // 3. undefined external symbols (sorted by name)
  
  // Sort the symbols by name, so that when we partition the symbols by scope
  // of definition, we won't have to sort by name within each partition.
  std::sort(SymbolTable.begin(), SymbolTable.end(), MachOSymCmp());

  // Parition the symbol table entries so that all local symbols come before 
  // all symbols with external linkage. { 1 | 2 3 }
  std::partition(SymbolTable.begin(), SymbolTable.end(), PartitionByLocal);
  
  // Advance iterator to beginning of external symbols and partition so that
  // all external symbols defined in this module come before all external
  // symbols defined elsewhere. { 1 | 2 | 3 }
  for (std::vector<MachOSym>::iterator I = SymbolTable.begin(),
         E = SymbolTable.end(); I != E; ++I) {
    if (!PartitionByLocal(*I)) {
      std::partition(I, E, PartitionByDefined);
      break;
    }
  }
  
  // Write out a leading zero byte when emitting string table, for n_strx == 0
  // which means an empty string.
  outbyte(StrT, 0);

  // The order of the string table is:
  // 1. strings for external symbols
  // 2. strings for local symbols
  // Since this is the opposite order from the symbol table, which we have just
  // sorted, we can walk the symbol table backwards to output the string table.
  for (std::vector<MachOSym>::reverse_iterator I = SymbolTable.rbegin(),
        E = SymbolTable.rend(); I != E; ++I) {
    if (I->GVName == "") {
      I->n_strx = 0;
    } else {
      I->n_strx = StrT.size();
      outstring(StrT, I->GVName, I->GVName.length()+1);
    }
  }

  for (std::vector<MachOSym>::iterator I = SymbolTable.begin(),
         E = SymbolTable.end(); I != E; ++I) {
    // Emit nlist to buffer
    outword(SymT, I->n_strx);
    outbyte(SymT, I->n_type);
    outbyte(SymT, I->n_sect);
    outhalf(SymT, I->n_desc);
    outaddr(SymT, I->n_value);
  }
}

MachOSym::MachOSym(const GlobalValue *gv, std::string name, uint8_t sect) :
  GV(gv), GVName(name), n_strx(0), n_type(sect == NO_SECT ? N_UNDF : N_SECT), 
  n_sect(sect), n_desc(0), n_value(0) {
  // FIXME: take a target machine, and then add the appropriate prefix for
  //        the linkage type based on the TargetAsmInfo
  switch (GV->getLinkage()) {
  default:
    assert(0 && "Unexpected linkage type!");
    break;
  case GlobalValue::WeakLinkage:
  case GlobalValue::LinkOnceLinkage:
    assert(!isa<Function>(gv) && "Unexpected linkage type for Function!");
  case GlobalValue::ExternalLinkage:
    n_type |= N_EXT;
    break;
  case GlobalValue::InternalLinkage:
    break;
  }
}