1 //===------ CFIInstrInserter.cpp - Insert additional CFI instructions -----===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 /// \file This pass verifies incoming and outgoing CFA information of basic 10 /// blocks. CFA information is information about offset and register set by CFI 11 /// directives, valid at the start and end of a basic block. This pass checks 12 /// that outgoing information of predecessors matches incoming information of 13 /// their successors. Then it checks if blocks have correct CFA calculation rule 14 /// set and inserts additional CFI instruction at their beginnings if they 15 /// don't. CFI instructions are inserted if basic blocks have incorrect offset 16 /// or register set by previous blocks, as a result of a non-linear layout of 17 /// blocks in a function. 18 //===----------------------------------------------------------------------===// 19 20 #include "llvm/ADT/DepthFirstIterator.h" 21 #include "llvm/CodeGen/MachineFunctionPass.h" 22 #include "llvm/CodeGen/MachineInstrBuilder.h" 23 #include "llvm/CodeGen/Passes.h" 24 #include "llvm/CodeGen/TargetFrameLowering.h" 25 #include "llvm/CodeGen/TargetInstrInfo.h" 26 #include "llvm/CodeGen/TargetSubtargetInfo.h" 27 #include "llvm/InitializePasses.h" 28 #include "llvm/MC/MCDwarf.h" 29 using namespace llvm; 30 31 static cl::opt<bool> VerifyCFI("verify-cfiinstrs", 32 cl::desc("Verify Call Frame Information instructions"), 33 cl::init(false), 34 cl::Hidden); 35 36 namespace { 37 class CFIInstrInserter : public MachineFunctionPass { 38 public: 39 static char ID; 40 41 CFIInstrInserter() : MachineFunctionPass(ID) { 42 initializeCFIInstrInserterPass(*PassRegistry::getPassRegistry()); 43 } 44 45 void getAnalysisUsage(AnalysisUsage &AU) const override { 46 AU.setPreservesAll(); 47 MachineFunctionPass::getAnalysisUsage(AU); 48 } 49 50 bool runOnMachineFunction(MachineFunction &MF) override { 51 if (!MF.needsFrameMoves()) 52 return false; 53 54 MBBVector.resize(MF.getNumBlockIDs()); 55 calculateCFAInfo(MF); 56 57 if (VerifyCFI) { 58 if (unsigned ErrorNum = verify(MF)) 59 report_fatal_error("Found " + Twine(ErrorNum) + 60 " in/out CFI information errors."); 61 } 62 bool insertedCFI = insertCFIInstrs(MF); 63 MBBVector.clear(); 64 return insertedCFI; 65 } 66 67 private: 68 struct MBBCFAInfo { 69 MachineBasicBlock *MBB; 70 /// Value of cfa offset valid at basic block entry. 71 int IncomingCFAOffset = -1; 72 /// Value of cfa offset valid at basic block exit. 73 int OutgoingCFAOffset = -1; 74 /// Value of cfa register valid at basic block entry. 75 unsigned IncomingCFARegister = 0; 76 /// Value of cfa register valid at basic block exit. 77 unsigned OutgoingCFARegister = 0; 78 /// Set of callee saved registers saved at basic block entry. 79 BitVector IncomingCSRSaved; 80 /// Set of callee saved registers saved at basic block exit. 81 BitVector OutgoingCSRSaved; 82 /// If in/out cfa offset and register values for this block have already 83 /// been set or not. 84 bool Processed = false; 85 }; 86 87 #define INVALID_REG UINT_MAX 88 #define INVALID_OFFSET INT_MAX 89 /// contains the location where CSR register is saved. 90 struct CSRSavedLocation { 91 CSRSavedLocation(std::optional<unsigned> R, std::optional<int> O) 92 : Reg(R), Offset(O) {} 93 std::optional<unsigned> Reg; 94 std::optional<int> Offset; 95 }; 96 97 /// Contains cfa offset and register values valid at entry and exit of basic 98 /// blocks. 99 std::vector<MBBCFAInfo> MBBVector; 100 101 /// Map the callee save registers to the locations where they are saved. 102 SmallDenseMap<unsigned, CSRSavedLocation, 16> CSRLocMap; 103 104 /// Calculate cfa offset and register values valid at entry and exit for all 105 /// basic blocks in a function. 106 void calculateCFAInfo(MachineFunction &MF); 107 /// Calculate cfa offset and register values valid at basic block exit by 108 /// checking the block for CFI instructions. Block's incoming CFA info remains 109 /// the same. 110 void calculateOutgoingCFAInfo(MBBCFAInfo &MBBInfo); 111 /// Update in/out cfa offset and register values for successors of the basic 112 /// block. 113 void updateSuccCFAInfo(MBBCFAInfo &MBBInfo); 114 115 /// Check if incoming CFA information of a basic block matches outgoing CFA 116 /// information of the previous block. If it doesn't, insert CFI instruction 117 /// at the beginning of the block that corrects the CFA calculation rule for 118 /// that block. 119 bool insertCFIInstrs(MachineFunction &MF); 120 /// Return the cfa offset value that should be set at the beginning of a MBB 121 /// if needed. The negated value is needed when creating CFI instructions that 122 /// set absolute offset. 123 int getCorrectCFAOffset(MachineBasicBlock *MBB) { 124 return MBBVector[MBB->getNumber()].IncomingCFAOffset; 125 } 126 127 void reportCFAError(const MBBCFAInfo &Pred, const MBBCFAInfo &Succ); 128 void reportCSRError(const MBBCFAInfo &Pred, const MBBCFAInfo &Succ); 129 /// Go through each MBB in a function and check that outgoing offset and 130 /// register of its predecessors match incoming offset and register of that 131 /// MBB, as well as that incoming offset and register of its successors match 132 /// outgoing offset and register of the MBB. 133 unsigned verify(MachineFunction &MF); 134 }; 135 } // namespace 136 137 char CFIInstrInserter::ID = 0; 138 INITIALIZE_PASS(CFIInstrInserter, "cfi-instr-inserter", 139 "Check CFA info and insert CFI instructions if needed", false, 140 false) 141 FunctionPass *llvm::createCFIInstrInserter() { return new CFIInstrInserter(); } 142 143 void CFIInstrInserter::calculateCFAInfo(MachineFunction &MF) { 144 // Initial CFA offset value i.e. the one valid at the beginning of the 145 // function. 146 int InitialOffset = 147 MF.getSubtarget().getFrameLowering()->getInitialCFAOffset(MF); 148 // Initial CFA register value i.e. the one valid at the beginning of the 149 // function. 150 Register InitialRegister = 151 MF.getSubtarget().getFrameLowering()->getInitialCFARegister(MF); 152 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo(); 153 unsigned NumRegs = TRI.getNumRegs(); 154 155 // Initialize MBBMap. 156 for (MachineBasicBlock &MBB : MF) { 157 MBBCFAInfo &MBBInfo = MBBVector[MBB.getNumber()]; 158 MBBInfo.MBB = &MBB; 159 MBBInfo.IncomingCFAOffset = InitialOffset; 160 MBBInfo.OutgoingCFAOffset = InitialOffset; 161 MBBInfo.IncomingCFARegister = InitialRegister; 162 MBBInfo.OutgoingCFARegister = InitialRegister; 163 MBBInfo.IncomingCSRSaved.resize(NumRegs); 164 MBBInfo.OutgoingCSRSaved.resize(NumRegs); 165 } 166 CSRLocMap.clear(); 167 168 // Set in/out cfa info for all blocks in the function. This traversal is based 169 // on the assumption that the first block in the function is the entry block 170 // i.e. that it has initial cfa offset and register values as incoming CFA 171 // information. 172 updateSuccCFAInfo(MBBVector[MF.front().getNumber()]); 173 } 174 175 void CFIInstrInserter::calculateOutgoingCFAInfo(MBBCFAInfo &MBBInfo) { 176 // Outgoing cfa offset set by the block. 177 int SetOffset = MBBInfo.IncomingCFAOffset; 178 // Outgoing cfa register set by the block. 179 unsigned SetRegister = MBBInfo.IncomingCFARegister; 180 MachineFunction *MF = MBBInfo.MBB->getParent(); 181 const std::vector<MCCFIInstruction> &Instrs = MF->getFrameInstructions(); 182 const TargetRegisterInfo &TRI = *MF->getSubtarget().getRegisterInfo(); 183 unsigned NumRegs = TRI.getNumRegs(); 184 BitVector CSRSaved(NumRegs), CSRRestored(NumRegs); 185 186 // Determine cfa offset and register set by the block. 187 for (MachineInstr &MI : *MBBInfo.MBB) { 188 if (MI.isCFIInstruction()) { 189 std::optional<unsigned> CSRReg; 190 std::optional<int> CSROffset; 191 unsigned CFIIndex = MI.getOperand(0).getCFIIndex(); 192 const MCCFIInstruction &CFI = Instrs[CFIIndex]; 193 switch (CFI.getOperation()) { 194 case MCCFIInstruction::OpDefCfaRegister: 195 SetRegister = CFI.getRegister(); 196 break; 197 case MCCFIInstruction::OpDefCfaOffset: 198 SetOffset = CFI.getOffset(); 199 break; 200 case MCCFIInstruction::OpAdjustCfaOffset: 201 SetOffset += CFI.getOffset(); 202 break; 203 case MCCFIInstruction::OpDefCfa: 204 SetRegister = CFI.getRegister(); 205 SetOffset = CFI.getOffset(); 206 break; 207 case MCCFIInstruction::OpOffset: 208 CSROffset = CFI.getOffset(); 209 break; 210 case MCCFIInstruction::OpRegister: 211 CSRReg = CFI.getRegister2(); 212 break; 213 case MCCFIInstruction::OpRelOffset: 214 CSROffset = CFI.getOffset() - SetOffset; 215 break; 216 case MCCFIInstruction::OpRestore: 217 CSRRestored.set(CFI.getRegister()); 218 break; 219 case MCCFIInstruction::OpLLVMDefAspaceCfa: 220 // TODO: Add support for handling cfi_def_aspace_cfa. 221 #ifndef NDEBUG 222 report_fatal_error( 223 "Support for cfi_llvm_def_aspace_cfa not implemented! Value of CFA " 224 "may be incorrect!\n"); 225 #endif 226 break; 227 case MCCFIInstruction::OpRememberState: 228 // TODO: Add support for handling cfi_remember_state. 229 #ifndef NDEBUG 230 report_fatal_error( 231 "Support for cfi_remember_state not implemented! Value of CFA " 232 "may be incorrect!\n"); 233 #endif 234 break; 235 case MCCFIInstruction::OpRestoreState: 236 // TODO: Add support for handling cfi_restore_state. 237 #ifndef NDEBUG 238 report_fatal_error( 239 "Support for cfi_restore_state not implemented! Value of CFA may " 240 "be incorrect!\n"); 241 #endif 242 break; 243 // Other CFI directives do not affect CFA value. 244 case MCCFIInstruction::OpUndefined: 245 case MCCFIInstruction::OpSameValue: 246 case MCCFIInstruction::OpEscape: 247 case MCCFIInstruction::OpWindowSave: 248 case MCCFIInstruction::OpNegateRAState: 249 case MCCFIInstruction::OpGnuArgsSize: 250 break; 251 } 252 if (CSRReg || CSROffset) { 253 auto It = CSRLocMap.find(CFI.getRegister()); 254 if (It == CSRLocMap.end()) { 255 CSRLocMap.insert( 256 {CFI.getRegister(), CSRSavedLocation(CSRReg, CSROffset)}); 257 } else if (It->second.Reg != CSRReg || It->second.Offset != CSROffset) { 258 llvm_unreachable("Different saved locations for the same CSR"); 259 } 260 CSRSaved.set(CFI.getRegister()); 261 } 262 } 263 } 264 265 MBBInfo.Processed = true; 266 267 // Update outgoing CFA info. 268 MBBInfo.OutgoingCFAOffset = SetOffset; 269 MBBInfo.OutgoingCFARegister = SetRegister; 270 271 // Update outgoing CSR info. 272 BitVector::apply([](auto x, auto y, auto z) { return (x | y) & ~z; }, 273 MBBInfo.OutgoingCSRSaved, MBBInfo.IncomingCSRSaved, CSRSaved, 274 CSRRestored); 275 } 276 277 void CFIInstrInserter::updateSuccCFAInfo(MBBCFAInfo &MBBInfo) { 278 SmallVector<MachineBasicBlock *, 4> Stack; 279 Stack.push_back(MBBInfo.MBB); 280 281 do { 282 MachineBasicBlock *Current = Stack.pop_back_val(); 283 MBBCFAInfo &CurrentInfo = MBBVector[Current->getNumber()]; 284 calculateOutgoingCFAInfo(CurrentInfo); 285 for (auto *Succ : CurrentInfo.MBB->successors()) { 286 MBBCFAInfo &SuccInfo = MBBVector[Succ->getNumber()]; 287 if (!SuccInfo.Processed) { 288 SuccInfo.IncomingCFAOffset = CurrentInfo.OutgoingCFAOffset; 289 SuccInfo.IncomingCFARegister = CurrentInfo.OutgoingCFARegister; 290 SuccInfo.IncomingCSRSaved = CurrentInfo.OutgoingCSRSaved; 291 Stack.push_back(Succ); 292 } 293 } 294 } while (!Stack.empty()); 295 } 296 297 bool CFIInstrInserter::insertCFIInstrs(MachineFunction &MF) { 298 const MBBCFAInfo *PrevMBBInfo = &MBBVector[MF.front().getNumber()]; 299 const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo(); 300 bool InsertedCFIInstr = false; 301 302 BitVector SetDifference; 303 for (MachineBasicBlock &MBB : MF) { 304 // Skip the first MBB in a function 305 if (MBB.getNumber() == MF.front().getNumber()) continue; 306 307 const MBBCFAInfo &MBBInfo = MBBVector[MBB.getNumber()]; 308 auto MBBI = MBBInfo.MBB->begin(); 309 DebugLoc DL = MBBInfo.MBB->findDebugLoc(MBBI); 310 311 // If the current MBB will be placed in a unique section, a full DefCfa 312 // must be emitted. 313 const bool ForceFullCFA = MBB.isBeginSection(); 314 315 if ((PrevMBBInfo->OutgoingCFAOffset != MBBInfo.IncomingCFAOffset && 316 PrevMBBInfo->OutgoingCFARegister != MBBInfo.IncomingCFARegister) || 317 ForceFullCFA) { 318 // If both outgoing offset and register of a previous block don't match 319 // incoming offset and register of this block, or if this block begins a 320 // section, add a def_cfa instruction with the correct offset and 321 // register for this block. 322 unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::cfiDefCfa( 323 nullptr, MBBInfo.IncomingCFARegister, getCorrectCFAOffset(&MBB))); 324 BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION)) 325 .addCFIIndex(CFIIndex); 326 InsertedCFIInstr = true; 327 } else if (PrevMBBInfo->OutgoingCFAOffset != MBBInfo.IncomingCFAOffset) { 328 // If outgoing offset of a previous block doesn't match incoming offset 329 // of this block, add a def_cfa_offset instruction with the correct 330 // offset for this block. 331 unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::cfiDefCfaOffset( 332 nullptr, getCorrectCFAOffset(&MBB))); 333 BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION)) 334 .addCFIIndex(CFIIndex); 335 InsertedCFIInstr = true; 336 } else if (PrevMBBInfo->OutgoingCFARegister != 337 MBBInfo.IncomingCFARegister) { 338 unsigned CFIIndex = 339 MF.addFrameInst(MCCFIInstruction::createDefCfaRegister( 340 nullptr, MBBInfo.IncomingCFARegister)); 341 BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION)) 342 .addCFIIndex(CFIIndex); 343 InsertedCFIInstr = true; 344 } 345 346 if (ForceFullCFA) { 347 MF.getSubtarget().getFrameLowering()->emitCalleeSavedFrameMovesFullCFA( 348 *MBBInfo.MBB, MBBI); 349 InsertedCFIInstr = true; 350 PrevMBBInfo = &MBBInfo; 351 continue; 352 } 353 354 BitVector::apply([](auto x, auto y) { return x & ~y; }, SetDifference, 355 PrevMBBInfo->OutgoingCSRSaved, MBBInfo.IncomingCSRSaved); 356 for (int Reg : SetDifference.set_bits()) { 357 unsigned CFIIndex = 358 MF.addFrameInst(MCCFIInstruction::createRestore(nullptr, Reg)); 359 BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION)) 360 .addCFIIndex(CFIIndex); 361 InsertedCFIInstr = true; 362 } 363 364 BitVector::apply([](auto x, auto y) { return x & ~y; }, SetDifference, 365 MBBInfo.IncomingCSRSaved, PrevMBBInfo->OutgoingCSRSaved); 366 for (int Reg : SetDifference.set_bits()) { 367 auto it = CSRLocMap.find(Reg); 368 assert(it != CSRLocMap.end() && "Reg should have an entry in CSRLocMap"); 369 unsigned CFIIndex; 370 CSRSavedLocation RO = it->second; 371 if (!RO.Reg && RO.Offset) { 372 CFIIndex = MF.addFrameInst( 373 MCCFIInstruction::createOffset(nullptr, Reg, *RO.Offset)); 374 } else if (RO.Reg && !RO.Offset) { 375 CFIIndex = MF.addFrameInst( 376 MCCFIInstruction::createRegister(nullptr, Reg, *RO.Reg)); 377 } else { 378 llvm_unreachable("RO.Reg and RO.Offset cannot both be valid/invalid"); 379 } 380 BuildMI(*MBBInfo.MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION)) 381 .addCFIIndex(CFIIndex); 382 InsertedCFIInstr = true; 383 } 384 385 PrevMBBInfo = &MBBInfo; 386 } 387 return InsertedCFIInstr; 388 } 389 390 void CFIInstrInserter::reportCFAError(const MBBCFAInfo &Pred, 391 const MBBCFAInfo &Succ) { 392 errs() << "*** Inconsistent CFA register and/or offset between pred and succ " 393 "***\n"; 394 errs() << "Pred: " << Pred.MBB->getName() << " #" << Pred.MBB->getNumber() 395 << " in " << Pred.MBB->getParent()->getName() 396 << " outgoing CFA Reg:" << Pred.OutgoingCFARegister << "\n"; 397 errs() << "Pred: " << Pred.MBB->getName() << " #" << Pred.MBB->getNumber() 398 << " in " << Pred.MBB->getParent()->getName() 399 << " outgoing CFA Offset:" << Pred.OutgoingCFAOffset << "\n"; 400 errs() << "Succ: " << Succ.MBB->getName() << " #" << Succ.MBB->getNumber() 401 << " incoming CFA Reg:" << Succ.IncomingCFARegister << "\n"; 402 errs() << "Succ: " << Succ.MBB->getName() << " #" << Succ.MBB->getNumber() 403 << " incoming CFA Offset:" << Succ.IncomingCFAOffset << "\n"; 404 } 405 406 void CFIInstrInserter::reportCSRError(const MBBCFAInfo &Pred, 407 const MBBCFAInfo &Succ) { 408 errs() << "*** Inconsistent CSR Saved between pred and succ in function " 409 << Pred.MBB->getParent()->getName() << " ***\n"; 410 errs() << "Pred: " << Pred.MBB->getName() << " #" << Pred.MBB->getNumber() 411 << " outgoing CSR Saved: "; 412 for (int Reg : Pred.OutgoingCSRSaved.set_bits()) 413 errs() << Reg << " "; 414 errs() << "\n"; 415 errs() << "Succ: " << Succ.MBB->getName() << " #" << Succ.MBB->getNumber() 416 << " incoming CSR Saved: "; 417 for (int Reg : Succ.IncomingCSRSaved.set_bits()) 418 errs() << Reg << " "; 419 errs() << "\n"; 420 } 421 422 unsigned CFIInstrInserter::verify(MachineFunction &MF) { 423 unsigned ErrorNum = 0; 424 for (auto *CurrMBB : depth_first(&MF)) { 425 const MBBCFAInfo &CurrMBBInfo = MBBVector[CurrMBB->getNumber()]; 426 for (MachineBasicBlock *Succ : CurrMBB->successors()) { 427 const MBBCFAInfo &SuccMBBInfo = MBBVector[Succ->getNumber()]; 428 // Check that incoming offset and register values of successors match the 429 // outgoing offset and register values of CurrMBB 430 if (SuccMBBInfo.IncomingCFAOffset != CurrMBBInfo.OutgoingCFAOffset || 431 SuccMBBInfo.IncomingCFARegister != CurrMBBInfo.OutgoingCFARegister) { 432 // Inconsistent offsets/registers are ok for 'noreturn' blocks because 433 // we don't generate epilogues inside such blocks. 434 if (SuccMBBInfo.MBB->succ_empty() && !SuccMBBInfo.MBB->isReturnBlock()) 435 continue; 436 reportCFAError(CurrMBBInfo, SuccMBBInfo); 437 ErrorNum++; 438 } 439 // Check that IncomingCSRSaved of every successor matches the 440 // OutgoingCSRSaved of CurrMBB 441 if (SuccMBBInfo.IncomingCSRSaved != CurrMBBInfo.OutgoingCSRSaved) { 442 reportCSRError(CurrMBBInfo, SuccMBBInfo); 443 ErrorNum++; 444 } 445 } 446 } 447 return ErrorNum; 448 } 449