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