lib/CodeGen/ELFCodeEmitter.cpp

   1 //===-- lib/CodeGen/ELFCodeEmitter.cpp ------------------------------------===//
   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 #define DEBUG_TYPE "elfce"
  11
  12 #include "ELF.h"
  13 #include "ELFWriter.h"
  14 #include "ELFCodeEmitter.h"
  15 #include "llvm/Constants.h"
  16 #include "llvm/DerivedTypes.h"
  17 #include "llvm/Function.h"
  18 #include "llvm/CodeGen/BinaryObject.h"
  19 #include "llvm/CodeGen/MachineConstantPool.h"
  20 #include "llvm/CodeGen/MachineFunction.h"
  21 #include "llvm/CodeGen/MachineJumpTableInfo.h"
  22 #include "llvm/CodeGen/MachineRelocation.h"
  23 #include "llvm/Target/TargetData.h"
  24 #include "llvm/Target/TargetELFWriterInfo.h"
  25 #include "llvm/Target/TargetMachine.h"
  26 #include "llvm/MC/MCAsmInfo.h"
  27 #include "llvm/Support/Debug.h"
  28 #include "llvm/Support/ErrorHandling.h"
  29 #include "llvm/Support/raw_ostream.h"
  30
  31 //===----------------------------------------------------------------------===//
  32 //                       ELFCodeEmitter Implementation
  33 //===----------------------------------------------------------------------===//
  34
  35 namespace llvm {
  36
  37 /// startFunction - This callback is invoked when a new machine function is
  38 /// about to be emitted.
  39 void ELFCodeEmitter::startFunction(MachineFunction &MF) {
  40   DEBUG(errs() << "processing function: "
  41         << MF.getFunction()->getName() << "\n");
  42
  43   // Get the ELF Section that this function belongs in.
  44   ES = &EW.getTextSection(MF.getFunction());
  45
  46   // Set the desired binary object to be used by the code emitters
  47   setBinaryObject(ES);
  48
  49   // Get the function alignment in bytes
  50   unsigned Align = (1 << MF.getAlignment());
  51
  52   // The function must start on its required alignment
  53   ES->emitAlignment(Align);
  54
  55   // Update the section alignment if needed.
  56   ES->Align = std::max(ES->Align, Align);
  57
  58   // Record the function start offset
  59   FnStartOff = ES->getCurrentPCOffset();
  60
  61   // Emit constant pool and jump tables to their appropriate sections.
  62   // They need to be emitted before the function because in some targets
  63   // the later may reference JT or CP entry address.
  64   emitConstantPool(MF.getConstantPool());
  65   emitJumpTables(MF.getJumpTableInfo());
  66 }
  67
  68 /// finishFunction - This callback is invoked after the function is completely
  69 /// finished.
  70 bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
  71   // Add a symbol to represent the function.
  72   const Function *F = MF.getFunction();
  73   ELFSym *FnSym = ELFSym::getGV(F, EW.getGlobalELFBinding(F), ELFSym::STT_FUNC,
  74                                 EW.getGlobalELFVisibility(F));
  75   FnSym->SectionIdx = ES->SectionIdx;
  76   FnSym->Size = ES->getCurrentPCOffset()-FnStartOff;
  77   EW.AddPendingGlobalSymbol(F, true);
  78
  79   // Offset from start of Section
  80   FnSym->Value = FnStartOff;
  81
  82   if (!F->hasPrivateLinkage())
  83     EW.SymbolList.push_back(FnSym);
  84
  85   // Patch up Jump Table Section relocations to use the real MBBs offsets
  86   // now that the MBB label offsets inside the function are known.
  87   if (!MF.getJumpTableInfo()->isEmpty()) {
  88     ELFSection &JTSection = EW.getJumpTableSection();
  89     for (std::vector<MachineRelocation>::iterator MRI = JTRelocations.begin(),
  90          MRE = JTRelocations.end(); MRI != MRE; ++MRI) {
  91       MachineRelocation &MR = *MRI;
  92       unsigned MBBOffset = getMachineBasicBlockAddress(MR.getBasicBlock());
  93       MR.setResultPointer((void*)MBBOffset);
  94       MR.setConstantVal(ES->SectionIdx);
  95       JTSection.addRelocation(MR);
  96     }
  97   }
  98
  99   // If we have emitted any relocations to function-specific objects such as
 100   // basic blocks, constant pools entries, or jump tables, record their
 101   // addresses now so that we can rewrite them with the correct addresses later
 102   for (unsigned i = 0, e = Relocations.size(); i != e; ++i) {
 103     MachineRelocation &MR = Relocations[i];
 104     intptr_t Addr;
 105     if (MR.isGlobalValue()) {
 106       EW.AddPendingGlobalSymbol(MR.getGlobalValue());
 107     } else if (MR.isExternalSymbol()) {
 108       EW.AddPendingExternalSymbol(MR.getExternalSymbol());
 109     } else if (MR.isBasicBlock()) {
 110       Addr = getMachineBasicBlockAddress(MR.getBasicBlock());
 111       MR.setConstantVal(ES->SectionIdx);
 112       MR.setResultPointer((void*)Addr);
 113     } else if (MR.isConstantPoolIndex()) {
 114       Addr = getConstantPoolEntryAddress(MR.getConstantPoolIndex());
 115       MR.setConstantVal(CPSections[MR.getConstantPoolIndex()]);
 116       MR.setResultPointer((void*)Addr);
 117     } else if (MR.isJumpTableIndex()) {
 118       ELFSection &JTSection = EW.getJumpTableSection();
 119       Addr = getJumpTableEntryAddress(MR.getJumpTableIndex());
 120       MR.setConstantVal(JTSection.SectionIdx);
 121       MR.setResultPointer((void*)Addr);
 122     } else {
 123       llvm_unreachable("Unhandled relocation type");
 124     }
 125     ES->addRelocation(MR);
 126   }
 127
 128   // Clear per-function data structures.
 129   JTRelocations.clear();
 130   Relocations.clear();
 131   CPLocations.clear();
 132   CPSections.clear();
 133   JTLocations.clear();
 134   MBBLocations.clear();
 135   return false;
 136 }
 137
 138 /// emitConstantPool - For each constant pool entry, figure out which section
 139 /// the constant should live in and emit the constant
 140 void ELFCodeEmitter::emitConstantPool(MachineConstantPool *MCP) {
 141   const std::vector<MachineConstantPoolEntry> &CP = MCP->getConstants();
 142   if (CP.empty()) return;
 143
 144   // TODO: handle PIC codegen
 145   assert(TM.getRelocationModel() != Reloc::PIC_ &&
 146          "PIC codegen not yet handled for elf constant pools!");
 147
 148   for (unsigned i = 0, e = CP.size(); i != e; ++i) {
 149     MachineConstantPoolEntry CPE = CP[i];
 150
 151     // Record the constant pool location and the section index
 152     ELFSection &CstPool = EW.getConstantPoolSection(CPE);
 153     CPLocations.push_back(CstPool.size());
 154     CPSections.push_back(CstPool.SectionIdx);
 155
 156     if (CPE.isMachineConstantPoolEntry())
 157       assert("CPE.isMachineConstantPoolEntry not supported yet");
 158
 159     // Emit the constant to constant pool section
 160     EW.EmitGlobalConstant(CPE.Val.ConstVal, CstPool);
 161   }
 162 }
 163
 164 /// emitJumpTables - Emit all the jump tables for a given jump table info
 165 /// record to the appropriate section.
 166 void ELFCodeEmitter::emitJumpTables(MachineJumpTableInfo *MJTI) {
 167   const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
 168   if (JT.empty()) return;
 169
 170   // FIXME: handle PIC codegen
 171   assert(TM.getRelocationModel() != Reloc::PIC_ &&
 172          "PIC codegen not yet handled for elf jump tables!");
 173
 174   const TargetELFWriterInfo *TEW = TM.getELFWriterInfo();
 175   unsigned EntrySize = MJTI->getEntrySize();
 176
 177   // Get the ELF Section to emit the jump table
 178   ELFSection &JTSection = EW.getJumpTableSection();
 179
 180   // For each JT, record its offset from the start of the section
 181   for (unsigned i = 0, e = JT.size(); i != e; ++i) {
 182     const std::vector<MachineBasicBlock*> &MBBs = JT[i].MBBs;
 183
 184     // Record JT 'i' offset in the JT section
 185     JTLocations.push_back(JTSection.size());
 186
 187     // Each MBB entry in the Jump table section has a relocation entry
 188     // against the current text section.
 189     for (unsigned mi = 0, me = MBBs.size(); mi != me; ++mi) {
 190       unsigned MachineRelTy = TEW->getAbsoluteLabelMachineRelTy();
 191       MachineRelocation MR =
 192         MachineRelocation::getBB(JTSection.size(), MachineRelTy, MBBs[mi]);
 193
 194       // Add the relocation to the Jump Table section
 195       JTRelocations.push_back(MR);
 196
 197       // Output placeholder for MBB in the JT section
 198       for (unsigned s=0; s < EntrySize; ++s)
 199         JTSection.emitByte(0);
 200     }
 201   }
 202 }
 203
 204 } // end namespace llvm