lib/CodeGen/CFIInstrInserter.cpp

   1 //===------ CFIInstrInserter.cpp - Insert additional CFI instructions -----===//
   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 /// \file This pass verifies incoming and outgoing CFA information of basic
  11 /// blocks. CFA information is information about offset and register set by CFI
  12 /// directives, valid at the start and end of a basic block. This pass checks
  13 /// that outgoing information of predecessors matches incoming information of
  14 /// their successors. Then it checks if blocks have correct CFA calculation rule
  15 /// set and inserts additional CFI instruction at their beginnings if they
  16 /// don't. CFI instructions are inserted if basic blocks have incorrect offset
  17 /// or register set by previous blocks, as a result of a non-linear layout of
  18 /// blocks in a function.
  19 //===----------------------------------------------------------------------===//
  20
  21 #include "llvm/ADT/DepthFirstIterator.h"
  22 #include "llvm/CodeGen/MachineFunctionPass.h"
  23 #include "llvm/CodeGen/MachineInstrBuilder.h"
  24 #include "llvm/CodeGen/MachineModuleInfo.h"
  25 #include "llvm/CodeGen/Passes.h"
  26 #include "llvm/CodeGen/TargetFrameLowering.h"
  27 #include "llvm/CodeGen/TargetInstrInfo.h"
  28 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  29 #include "llvm/Target/TargetMachine.h"
  30 using namespace llvm;
  31
  32 static cl::opt<bool> VerifyCFI("verify-cfiinstrs",
  33     cl::desc("Verify Call Frame Information instructions"),
  34     cl::init(false),
  35     cl::Hidden);
  36
  37 namespace {
  38 class CFIInstrInserter : public MachineFunctionPass {
  39  public:
  40   static char ID;
  41
  42   CFIInstrInserter() : MachineFunctionPass(ID) {
  43     initializeCFIInstrInserterPass(*PassRegistry::getPassRegistry());
  44   }
  45
  46   void getAnalysisUsage(AnalysisUsage &AU) const override {
  47     AU.setPreservesAll();
  48     MachineFunctionPass::getAnalysisUsage(AU);
  49   }
  50
  51   bool runOnMachineFunction(MachineFunction &MF) override {
  52     if (!MF.getMMI().hasDebugInfo() &&
  53         !MF.getFunction().needsUnwindTableEntry())
  54       return false;
  55
  56     MBBVector.resize(MF.getNumBlockIDs());
  57     calculateCFAInfo(MF);
  58
  59     if (VerifyCFI) {
  60       if (unsigned ErrorNum = verify(MF))
  61         report_fatal_error("Found " + Twine(ErrorNum) +
  62                            " in/out CFI information errors.");
  63     }
  64     bool insertedCFI = insertCFIInstrs(MF);
  65     MBBVector.clear();
  66     return insertedCFI;
  67   }
  68
  69  private:
  70   struct MBBCFAInfo {
  71     MachineBasicBlock *MBB;
  72     /// Value of cfa offset valid at basic block entry.
  73     int IncomingCFAOffset = -1;
  74     /// Value of cfa offset valid at basic block exit.
  75     int OutgoingCFAOffset = -1;
  76     /// Value of cfa register valid at basic block entry.
  77     unsigned IncomingCFARegister = 0;
  78     /// Value of cfa register valid at basic block exit.
  79     unsigned OutgoingCFARegister = 0;
  80     /// If in/out cfa offset and register values for this block have already
  81     /// been set or not.
  82     bool Processed = false;
  83   };
  84
  85   /// Contains cfa offset and register values valid at entry and exit of basic
  86   /// blocks.
  87   std::vector<MBBCFAInfo> MBBVector;
  88
  89   /// Calculate cfa offset and register values valid at entry and exit for all
  90   /// basic blocks in a function.
  91   void calculateCFAInfo(MachineFunction &MF);
  92   /// Calculate cfa offset and register values valid at basic block exit by
  93   /// checking the block for CFI instructions. Block's incoming CFA info remains
  94   /// the same.
  95   void calculateOutgoingCFAInfo(MBBCFAInfo &MBBInfo);
  96   /// Update in/out cfa offset and register values for successors of the basic
  97   /// block.
  98   void updateSuccCFAInfo(MBBCFAInfo &MBBInfo);
  99
 100   /// Check if incoming CFA information of a basic block matches outgoing CFA
 101   /// information of the previous block. If it doesn't, insert CFI instruction
 102   /// at the beginning of the block that corrects the CFA calculation rule for
 103   /// that block.
 104   bool insertCFIInstrs(MachineFunction &MF);
 105   /// Return the cfa offset value that should be set at the beginning of a MBB
 106   /// if needed. The negated value is needed when creating CFI instructions that
 107   /// set absolute offset.
 108   int getCorrectCFAOffset(MachineBasicBlock *MBB) {
 109     return -MBBVector[MBB->getNumber()].IncomingCFAOffset;
 110   }
 111
 112   void report(const MBBCFAInfo &Pred, const MBBCFAInfo &Succ);
 113   /// Go through each MBB in a function and check that outgoing offset and
 114   /// register of its predecessors match incoming offset and register of that
 115   /// MBB, as well as that incoming offset and register of its successors match
 116   /// outgoing offset and register of the MBB.
 117   unsigned verify(MachineFunction &MF);
 118 };
 119 }  // namespace
 120
 121 char CFIInstrInserter::ID = 0;
 122 INITIALIZE_PASS(CFIInstrInserter, "cfi-instr-inserter",
 123                 "Check CFA info and insert CFI instructions if needed", false,
 124                 false)
 125 FunctionPass *llvm::createCFIInstrInserter() { return new CFIInstrInserter(); }
 126
 127 void CFIInstrInserter::calculateCFAInfo(MachineFunction &MF) {
 128   // Initial CFA offset value i.e. the one valid at the beginning of the
 129   // function.
 130   int InitialOffset =
 131       MF.getSubtarget().getFrameLowering()->getInitialCFAOffset(MF);
 132   // Initial CFA register value i.e. the one valid at the beginning of the
 133   // function.
 134   unsigned InitialRegister =
 135       MF.getSubtarget().getFrameLowering()->getInitialCFARegister(MF);
 136
 137   // Initialize MBBMap.
 138   for (MachineBasicBlock &MBB : MF) {
 139     MBBCFAInfo MBBInfo;
 140     MBBInfo.MBB = &MBB;
 141     MBBInfo.IncomingCFAOffset = InitialOffset;
 142     MBBInfo.OutgoingCFAOffset = InitialOffset;
 143     MBBInfo.IncomingCFARegister = InitialRegister;
 144     MBBInfo.OutgoingCFARegister = InitialRegister;
 145     MBBVector[MBB.getNumber()] = MBBInfo;
 146   }
 147
 148   // Set in/out cfa info for all blocks in the function. This traversal is based
 149   // on the assumption that the first block in the function is the entry block
 150   // i.e. that it has initial cfa offset and register values as incoming CFA
 151   // information.
 152   for (MachineBasicBlock &MBB : MF) {
 153     if (MBBVector[MBB.getNumber()].Processed) continue;
 154     updateSuccCFAInfo(MBBVector[MBB.getNumber()]);
 155   }
 156 }
 157
 158 void CFIInstrInserter::calculateOutgoingCFAInfo(MBBCFAInfo &MBBInfo) {
 159   // Outgoing cfa offset set by the block.
 160   int SetOffset = MBBInfo.IncomingCFAOffset;
 161   // Outgoing cfa register set by the block.
 162   unsigned SetRegister = MBBInfo.IncomingCFARegister;
 163   const std::vector<MCCFIInstruction> &Instrs =
 164       MBBInfo.MBB->getParent()->getFrameInstructions();
 165
 166   // Determine cfa offset and register set by the block.
 167   for (MachineInstr &MI : *MBBInfo.MBB) {
 168     if (MI.isCFIInstruction()) {
 169       unsigned CFIIndex = MI.getOperand(0).getCFIIndex();
 170       const MCCFIInstruction &CFI = Instrs[CFIIndex];
 171       switch (CFI.getOperation()) {
 172       case MCCFIInstruction::OpDefCfaRegister:
 173         SetRegister = CFI.getRegister();
 174         break;
 175       case MCCFIInstruction::OpDefCfaOffset:
 176         SetOffset = CFI.getOffset();
 177         break;
 178       case MCCFIInstruction::OpAdjustCfaOffset:
 179         SetOffset += CFI.getOffset();
 180         break;
 181       case MCCFIInstruction::OpDefCfa:
 182         SetRegister = CFI.getRegister();
 183         SetOffset = CFI.getOffset();
 184         break;
 185       case MCCFIInstruction::OpRememberState:
 186         // TODO: Add support for handling cfi_remember_state.
 187 #ifndef NDEBUG
 188         report_fatal_error(
 189             "Support for cfi_remember_state not implemented! Value of CFA "
 190             "may be incorrect!\n");
 191 #endif
 192         break;
 193       case MCCFIInstruction::OpRestoreState:
 194         // TODO: Add support for handling cfi_restore_state.
 195 #ifndef NDEBUG
 196         report_fatal_error(
 197             "Support for cfi_restore_state not implemented! Value of CFA may "
 198             "be incorrect!\n");
 199 #endif
 200         break;
 201       // Other CFI directives do not affect CFA value.
 202       case MCCFIInstruction::OpSameValue:
 203       case MCCFIInstruction::OpOffset:
 204       case MCCFIInstruction::OpRelOffset:
 205       case MCCFIInstruction::OpEscape:
 206       case MCCFIInstruction::OpRestore:
 207       case MCCFIInstruction::OpUndefined:
 208       case MCCFIInstruction::OpRegister:
 209       case MCCFIInstruction::OpWindowSave:
 210       case MCCFIInstruction::OpGnuArgsSize:
 211         break;
 212       }
 213     }
 214   }
 215
 216   MBBInfo.Processed = true;
 217
 218   // Update outgoing CFA info.
 219   MBBInfo.OutgoingCFAOffset = SetOffset;
 220   MBBInfo.OutgoingCFARegister = SetRegister;
 221 }
 222
 223 void CFIInstrInserter::updateSuccCFAInfo(MBBCFAInfo &MBBInfo) {
 224   SmallVector<MachineBasicBlock *, 4> Stack;
 225   Stack.push_back(MBBInfo.MBB);
 226
 227   do {
 228     MachineBasicBlock *Current = Stack.pop_back_val();
 229     MBBCFAInfo &CurrentInfo = MBBVector[Current->getNumber()];
 230     if (CurrentInfo.Processed)
 231       continue;
 232
 233     calculateOutgoingCFAInfo(CurrentInfo);
 234     for (auto *Succ : CurrentInfo.MBB->successors()) {
 235       MBBCFAInfo &SuccInfo = MBBVector[Succ->getNumber()];
 236       if (!SuccInfo.Processed) {
 237         SuccInfo.IncomingCFAOffset = CurrentInfo.OutgoingCFAOffset;
 238         SuccInfo.IncomingCFARegister = CurrentInfo.OutgoingCFARegister;
 239         Stack.push_back(Succ);
 240       }
 241     }
 242   } while (!Stack.empty());
 243 }
 244
 245 bool CFIInstrInserter::insertCFIInstrs(MachineFunction &MF) {
 246   const MBBCFAInfo *PrevMBBInfo = &MBBVector[MF.front().getNumber()];
 247   const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
 248   bool InsertedCFIInstr = false;
 249
 250   for (MachineBasicBlock &MBB : MF) {
 251     // Skip the first MBB in a function
 252     if (MBB.getNumber() == MF.front().getNumber()) continue;
 253
 254     const MBBCFAInfo &MBBInfo = MBBVector[MBB.getNumber()];
 255     auto MBBI = MBBInfo.MBB->begin();
 256     DebugLoc DL = MBBInfo.MBB->findDebugLoc(MBBI);
 257
 258     if (PrevMBBInfo->OutgoingCFAOffset != MBBInfo.IncomingCFAOffset) {
 259       // If both outgoing offset and register of a previous block don't match
 260       // incoming offset and register of this block, add a def_cfa instruction
 261       // with the correct offset and register for this block.
 262       if (PrevMBBInfo->OutgoingCFARegister != MBBInfo.IncomingCFARegister) {
 263         unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createDefCfa(
 264             nullptr, MBBInfo.IncomingCFARegister, getCorrectCFAOffset(&MBB)));
 265         BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
 266             .addCFIIndex(CFIIndex);
 267         // If outgoing offset of a previous block doesn't match incoming offset
 268         // of this block, add a def_cfa_offset instruction with the correct
 269         // offset for this block.
 270       } else {
 271         unsigned CFIIndex =
 272             MF.addFrameInst(MCCFIInstruction::createDefCfaOffset(
 273                 nullptr, getCorrectCFAOffset(&MBB)));
 274         BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
 275             .addCFIIndex(CFIIndex);
 276       }
 277       InsertedCFIInstr = true;
 278       // If outgoing register of a previous block doesn't match incoming
 279       // register of this block, add a def_cfa_register instruction with the
 280       // correct register for this block.
 281     } else if (PrevMBBInfo->OutgoingCFARegister !=
 282                MBBInfo.IncomingCFARegister) {
 283       unsigned CFIIndex =
 284           MF.addFrameInst(MCCFIInstruction::createDefCfaRegister(
 285               nullptr, MBBInfo.IncomingCFARegister));
 286       BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
 287           .addCFIIndex(CFIIndex);
 288       InsertedCFIInstr = true;
 289     }
 290     PrevMBBInfo = &MBBInfo;
 291   }
 292   return InsertedCFIInstr;
 293 }
 294
 295 void CFIInstrInserter::report(const MBBCFAInfo &Pred, const MBBCFAInfo &Succ) {
 296   errs() << "*** Inconsistent CFA register and/or offset between pred and succ "
 297             "***\n";
 298   errs() << "Pred: " << Pred.MBB->getName() << " #" << Pred.MBB->getNumber()
 299          << " in " << Pred.MBB->getParent()->getName()
 300          << " outgoing CFA Reg:" << Pred.OutgoingCFARegister << "\n";
 301   errs() << "Pred: " << Pred.MBB->getName() << " #" << Pred.MBB->getNumber()
 302          << " in " << Pred.MBB->getParent()->getName()
 303          << " outgoing CFA Offset:" << Pred.OutgoingCFAOffset << "\n";
 304   errs() << "Succ: " << Succ.MBB->getName() << " #" << Succ.MBB->getNumber()
 305          << " incoming CFA Reg:" << Succ.IncomingCFARegister << "\n";
 306   errs() << "Succ: " << Succ.MBB->getName() << " #" << Succ.MBB->getNumber()
 307          << " incoming CFA Offset:" << Succ.IncomingCFAOffset << "\n";
 308 }
 309
 310 unsigned CFIInstrInserter::verify(MachineFunction &MF) {
 311   unsigned ErrorNum = 0;
 312   for (auto *CurrMBB : depth_first(&MF)) {
 313     const MBBCFAInfo &CurrMBBInfo = MBBVector[CurrMBB->getNumber()];
 314     for (MachineBasicBlock *Succ : CurrMBB->successors()) {
 315       const MBBCFAInfo &SuccMBBInfo = MBBVector[Succ->getNumber()];
 316       // Check that incoming offset and register values of successors match the
 317       // outgoing offset and register values of CurrMBB
 318       if (SuccMBBInfo.IncomingCFAOffset != CurrMBBInfo.OutgoingCFAOffset ||
 319           SuccMBBInfo.IncomingCFARegister != CurrMBBInfo.OutgoingCFARegister) {
 320         // Inconsistent offsets/registers are ok for 'noreturn' blocks because
 321         // we don't generate epilogues inside such blocks.
 322         if (SuccMBBInfo.MBB->succ_empty() && !SuccMBBInfo.MBB->isReturnBlock())
 323           continue;
 324         report(CurrMBBInfo, SuccMBBInfo);
 325         ErrorNum++;
 326       }
 327     }
 328   }
 329   return ErrorNum;
 330 }