path: root/lib/CodeGen/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/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/MC/MCAsmInfo.h"
#include "llvm/Target/Mangler.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/raw_ostream.h"
#include "llvm/ADT/SmallString.h"
using namespace llvm;

char ELFWriter::ID = 0;

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

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

  MAI = TM.getMCAsmInfo();
  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;

  while(!SymbolList.empty()) {
    delete SymbolList.back(); 
    SymbolList.pop_back();
  }

  while(!PrivateSyms.empty()) {
    delete PrivateSyms.back(); 
    PrivateSyms.pop_back();
  }

  while(!SectionList.empty()) {
    delete SectionList.back(); 
    SectionList.pop_back();
  }

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

// 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(OutContext, *TM.getTargetData());

  // 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(ELF::EV_CURRENT);   // e_ident[EI_VERSION]
  ElfHdr.emitAlignment(16);           // e_ident[EI_NIDENT-EI_PAD]

  ElfHdr.emitWord16(ELF::ET_REL);        // e_type
  ElfHdr.emitWord16(TEW->getEMachine()); // e_machine = target
  ElfHdr.emitWord32(ELF::EV_CURRENT);    // e_version