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(dbgs() << "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   if (MF.getJumpTableInfo())
  66     emitJumpTables(MF.getJumpTableInfo());
  67 }
  68
  69 /// finishFunction - This callback is invoked after the function is completely
  70 /// finished.
  71 bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
  72   // Add a symbol to represent the function.
  73   const Function *F = MF.getFunction();
  74   ELFSym *FnSym = ELFSym::getGV(F, EW.getGlobalELFBinding(F), ELF::STT_FUNC,
  75                                 EW.getGlobalELFVisibility(F));
  76   FnSym->SectionIdx = ES->SectionIdx;
  77   FnSym->Size = ES->getCurrentPCOffset()-FnStartOff;
  78   EW.AddPendingGlobalSymbol(F, true);
  79
  80   // Offset from start of Section
  81   FnSym->Value = FnStartOff;
  82
  83   if (!F->hasPrivateLinkage())
  84     EW.SymbolList.push_back(FnSym);
  85
  86   // Patch up Jump Table Section relocations to use the real MBBs offsets
  87   // now that the MBB label offsets inside the function are known.
  88   if (MF.getJumpTableInfo()) {
  89     ELFSection &JTSection = EW.getJumpTableSection();
  90     for (std::vector<MachineRelocation>::iterator MRI = JTRelocations.begin(),
  91          MRE = JTRelocations.end(); MRI != MRE; ++MRI) {
  92       MachineRelocation &MR = *MRI;
  93       uintptr_t MBBOffset = getMachineBasicBlockAddress(MR.getBasicBlock());
  94       MR.setResultPointer((void*)MBBOffset);
  95       MR.setConstantVal(ES->SectionIdx);
  96       JTSection.addRelocation(MR);
  97     }
  98   }
  99
 100   // If we have emitted any relocations to function-specific objects such as
 101   // basic blocks, constant pools entries, or jump tables, record their
 102   // addresses now so that we can rewrite them with the correct addresses later
 103   for (unsigned i = 0, e = Relocations.size(); i != e; ++i) {
 104     MachineRelocation &MR = Relocations[i];
 105     intptr_t Addr;
 106     if (MR.isGlobalValue()) {
 107       EW.AddPendingGlobalSymbol(MR.getGlobalValue());
 108     } else if (MR.isExternalSymbol()) {
 109       EW.AddPendingExternalSymbol(MR.getExternalSymbol());
 110     } else if (MR.isBasicBlock()) {
 111       Addr = getMachineBasicBlockAddress(MR.getBasicBlock());
 112       MR.setConstantVal(ES->SectionIdx);
 113       MR.setResultPointer((void*)Addr);
 114     } else if (MR.isConstantPoolIndex()) {
 115       Addr = getConstantPoolEntryAddress(MR.getConstantPoolIndex());
 116       MR.setConstantVal(CPSections[MR.getConstantPoolIndex()]);
 117       MR.setResultPointer((void*)Addr);
 118     } else if (MR.isJumpTableIndex()) {
 119       ELFSection &JTSection = EW.getJumpTableSection();
 120       Addr = getJumpTableEntryAddress(MR.getJumpTableIndex());
 121       MR.setConstantVal(JTSection.SectionIdx);
 122       MR.setResultPointer((void*)Addr);
 123     } else {
 124       llvm_unreachable("Unhandled relocation type");
 125     }
 126     ES->addRelocation(MR);
 127   }
 128
 129   // Clear per-function data structures.
 130   JTRelocations.clear();
 131   Relocations.clear();
 132   CPLocations.clear();
 133   CPSections.clear();
 134   JTLocations.clear();
 135   MBBLocations.clear();
 136   return false;
 137 }
 138
 139 /// emitConstantPool - For each constant pool entry, figure out which section
 140 /// the constant should live in and emit the constant
 141 void ELFCodeEmitter::emitConstantPool(MachineConstantPool *MCP) {
 142   const std::vector<MachineConstantPoolEntry> &CP = MCP->getConstants();
 143   if (CP.empty()) return;
 144
 145   // TODO: handle PIC codegen
 146   assert(TM.getRelocationModel() != Reloc::PIC_ &&
 147          "PIC codegen not yet handled for elf constant pools!");
 148
 149   for (unsigned i = 0, e = CP.size(); i != e; ++i) {
 150     MachineConstantPoolEntry CPE = CP[i];
 151
 152     // Record the constant pool location and the section index
 153     ELFSection &CstPool = EW.getConstantPoolSection(CPE);
 154     CPLocations.push_back(CstPool.size());
 155     CPSections.push_back(CstPool.SectionIdx);
 156
 157     if (CPE.isMachineConstantPoolEntry())
 158       assert("CPE.isMachineConstantPoolEntry not supported yet");
 159
 160     // Emit the constant to constant pool section
 161     EW.EmitGlobalConstant(CPE.Val.ConstVal, CstPool);
 162   }
 163 }
 164
 165 /// emitJumpTables - Emit all the jump tables for a given jump table info
 166 /// record to the appropriate section.
 167 void ELFCodeEmitter::emitJumpTables(MachineJumpTableInfo *MJTI) {
 168   const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
 169   if (JT.empty()) return;
 170
 171   // FIXME: handle PIC codegen
 172   assert(TM.getRelocationModel() != Reloc::PIC_ &&
 173          "PIC codegen not yet handled for elf jump tables!");
 174
 175   const TargetELFWriterInfo *TEW = TM.getELFWriterInfo();
 176   unsigned EntrySize = 4; //MJTI->getEntrySize();
 177
 178   // Get the ELF Section to emit the jump table
 179   ELFSection &JTSection = EW.getJumpTableSection();
 180
 181   // For each JT, record its offset from the start of the section
 182   for (unsigned i = 0, e = JT.size(); i != e; ++i) {
 183     const std::vector<MachineBasicBlock*> &MBBs = JT[i].MBBs;
 184
 185     // Record JT 'i' offset in the JT section
 186     JTLocations.push_back(JTSection.size());
 187
 188     // Each MBB entry in the Jump table section has a relocation entry
 189     // against the current text section.
 190     for (unsigned mi = 0, me = MBBs.size(); mi != me; ++mi) {
 191       unsigned MachineRelTy = TEW->getAbsoluteLabelMachineRelTy();
 192       MachineRelocation MR =
 193         MachineRelocation::getBB(JTSection.size(), MachineRelTy, MBBs[mi]);
 194
 195       // Add the relocation to the Jump Table section
 196       JTRelocations.push_back(MR);
 197
 198       // Output placeholder for MBB in the JT section
 199       for (unsigned s=0; s < EntrySize; ++s)
 200         JTSection.emitByte(0);
 201     }
 202   }
 203 }
 204
 205 } // end namespace llvm