ELFWriter.cpp

//===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the target-independent ELF writer.  This file writes out
// the ELF file in the following order:
//
//  #1. ELF Header
//  #2. '.text' section
//  #3. '.data' section
//  #4. '.bss' section  (conceptual position in file)
//  ...
//  #X. '.shstrtab' section
//  #Y. Section Table
//
// The entries in the section table are laid out as:
//  #0. Null entry [required]
//  #1. ".text" entry - the program code
//  #2. ".data" entry - global variables with initializers.     [ if needed ]
//  #3. ".bss" entry  - global variables without initializers.  [ if needed ]
//  ...
//  #N. ".shstrtab" entry - String table for the section names.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "elfwriter"
#include "ELF.h"
#include "ELFWriter.h"
#include "ELFCodeEmitter.h"
#include "llvm/Constants.h"
#include "llvm/Module.h"
#include "llvm/PassManager.h"
#include "llvm/DerivedTypes.h"
#include "llvm/CodeGen/BinaryObject.h"
#include "llvm/CodeGen/FileWriters.h"
#include "llvm/CodeGen/MachineCodeEmitter.h"
#include "llvm/CodeGen/ObjectCodeEmitter.h"
#include "llvm/CodeGen/MachineCodeEmitter.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/Target/TargetAsmInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetELFWriterInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Mangler.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;

char ELFWriter::ID = 0;

/// AddELFWriter - Add the ELF writer to the function pass manager
ObjectCodeEmitter *llvm::AddELFWriter(PassManagerBase &PM,
                                      raw_ostream &O,
                                      TargetMachine &TM) {
  ELFWriter *EW = new ELFWriter(O, TM);
  PM.add(EW);
  return EW->getObjectCodeEmitter();
}

//===----------------------------------------------------------------------===//
//                          ELFWriter Implementation
//===----------------------------------------------------------------------===//

ELFWriter::ELFWriter(raw_ostream &o, TargetMachine &tm)
  : MachineFunctionPass(&ID), O(o), TM(tm),
    OutContext(*new MCContext()),
    TLOF(TM.getTargetLowering()->getObjFileLowering()),
    is64Bit(TM.getTargetData()->getPointerSizeInBits() == 64),
    isLittleEndian(TM.getTargetData()->isLittleEndian()),
    ElfHdr(isLittleEndian, is64Bit) {

  TAI = TM.getTargetAsmInfo();
  TEW = TM.getELFWriterInfo();

  // Create the object code emitter object for this target.
  ElfCE = new ELFCodeEmitter(*this);

  // Inital number of sections
  NumSections = 0;
}

ELFWriter::~ELFWriter() {
  delete ElfCE;
  delete &OutContext;
}

// doInitialization - Emit the file header and all of the global variables for
// the module to the ELF file.
bool ELFWriter::doInitialization(Module &M) {
  // Initialize TargetLoweringObjectFile.
  const_cast<TargetLoweringObjectFile&>(TLOF).Initialize(OutContext, TM);
  
  Mang = new Mangler(M);

  // ELF Header
  // ----------
  // Fields e_shnum e_shstrndx are only known after all section have
  // been emitted. They locations in the ouput buffer are recorded so
  // to be patched up later.
  //
  // Note
  // ----
  // emitWord method behaves differently for ELF32 and ELF64, writing
  // 4 bytes in the former and 8 in the last for *_off and *_addr elf types

  ElfHdr.emitByte(0x7f); // e_ident[EI_MAG0]
  ElfHdr.emitByte('E');  // e_ident[EI_MAG1]
  ElfHdr.emitByte('L');  // e_ident[EI_MAG2]
  ElfHdr.emitByte('F');  // e_ident[EI_MAG3]

  ElfHdr.emitByte(TEW->getEIClass()); // e_ident[EI_CLASS]
  ElfHdr.emitByte(TEW->getEIData());  // e_ident[EI_DATA]
  ElfHdr.emitByte(EV_CURRENT);        // e_ident[EI_VERSION]
  ElfHdr.emitAlignment(16);           // e_ident[EI_NIDENT-EI_PAD]

  ElfHdr.emitWord16(ET_REL);             // e_type
  ElfHdr.emitWord16(TEW->getEMachine()); // e_machine = target
  ElfHdr.emitWord32(EV_CURRENT);         // e_version
  ElfHdr.emitWord(0);                    // e_entry, no entry point in .o file
  ElfHdr.emitWord(0);                    // e_phoff, no program header for .o
  ELFHdr_e_shoff_Offset = ElfHdr.size();
  ElfHdr.emitWord(0);                    // e_shoff = sec hdr table off in bytes
  ElfHdr.emitWord32(TEW->getEFlags());   // e_flags = whatever the target wants
  ElfHdr.emitWord16(TEW->getHdrSize());  // e_ehsize = ELF header size
  ElfHdr.emitWord16(0);                  // e_phentsize = prog header entry size
  ElfHdr.emitWord16(0);                  // e_phnum = # prog header entries = 0

  // e_shentsize = Section header entry size
  ElfHdr.emitWord16(TEW->getSHdrSize());

  // e_shnum     = # of section header ents
  ELFHdr_e_shnum_Offset = ElfHdr.size();
  ElfHdr.emitWord16(0); // Placeholder

  // e_shstrndx  = Section # of '.shstrtab'
  ELFHdr_e_shstrndx_Offset = ElfHdr.size();
  ElfHdr.emitWord16(0); // Placeholder

  // Add the null section, which is required to be first in the file.
  getNullSection();

  // The first entry in the symtab is the null symbol and the second
  // is a local symbol containing the module/file name
  SymbolList.push_back(new ELFSym());
  SymbolList.push_back(ELFSym::getFileSym());

  return false;
}

// AddPendingGlobalSymbol - Add a global to be processed and to
// the global symbol lookup, use a zero index because the table
// index will be determined later.
void ELFWriter::AddPendingGlobalSymbol(const GlobalValue *GV, 
                                       bool AddToLookup /* = false */) {
  PendingGlobals.insert(GV);
  if (AddToLookup) 
    GblSymLookup[GV] = 0;
}

// AddPendingExternalSymbol - Add the external to be processed
// and to the external symbol lookup, use a zero index because
// the symbol table index will be determined later.
void ELFWriter::AddPendingExternalSymbol(const char *External) {
  PendingExternals.insert(External);
  ExtSymLookup[External] = 0;
}

ELFSection &ELFWriter::getDataSection() {
  const MCSectionELF *Data = (const MCSectionELF *)TLOF.getDataSection();
  return getSection(Data->getSectionName(), Data->getType(), 
                    Data->getFlags(), 4);
}

ELFSection &ELFWriter::getBSSSection() {
  const MCSectionELF *BSS = (const MCSectionELF *)TLOF.getBSSSection();
  return getSection(BSS->getSectionName(), BSS->getType(), BSS->getFlags(), 4);
}

// getCtorSection - Get the static constructor section
ELFSection &ELFWriter::getCtorSection() {
  const MCSectionELF *Ctor = (const MCSectionELF *)TLOF.getStaticCtorSection();
  return getSection(Ctor->getSectionName(), Ctor->getType(), Ctor->getFlags()); 
}

// getDtorSection - Get the static destructor section
ELFSection &ELFWriter::getDtorSection() {
  const MCSectionELF *Dtor = (const MCSectionELF *)TLOF.getStaticDtorSection();
  return getSection(Dtor->getSectionName(), Dtor->getType(), Dtor->getFlags());
}