1 //===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind 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 // This transformation is designed for use by code generators which use SjLj 10 // based exception handling. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/ADT/SetVector.h" 15 #include "llvm/ADT/SmallPtrSet.h" 16 #include "llvm/ADT/SmallVector.h" 17 #include "llvm/ADT/Statistic.h" 18 #include "llvm/Transforms/Utils/Local.h" 19 #include "llvm/CodeGen/Passes.h" 20 #include "llvm/IR/Constants.h" 21 #include "llvm/IR/DataLayout.h" 22 #include "llvm/IR/DerivedTypes.h" 23 #include "llvm/IR/IRBuilder.h" 24 #include "llvm/IR/Instructions.h" 25 #include "llvm/IR/Intrinsics.h" 26 #include "llvm/IR/Module.h" 27 #include "llvm/Pass.h" 28 #include "llvm/Support/Debug.h" 29 #include "llvm/Support/raw_ostream.h" 30 using namespace llvm; 31 32 #define DEBUG_TYPE "sjljehprepare" 33 34 STATISTIC(NumInvokes, "Number of invokes replaced"); 35 STATISTIC(NumSpilled, "Number of registers live across unwind edges"); 36 37 namespace { 38 class SjLjEHPrepare : public FunctionPass { 39 Type *doubleUnderDataTy; 40 Type *doubleUnderJBufTy; 41 Type *FunctionContextTy; 42 FunctionCallee RegisterFn; 43 FunctionCallee UnregisterFn; 44 Function *BuiltinSetupDispatchFn; 45 Function *FrameAddrFn; 46 Function *StackAddrFn; 47 Function *StackRestoreFn; 48 Function *LSDAAddrFn; 49 Function *CallSiteFn; 50 Function *FuncCtxFn; 51 AllocaInst *FuncCtx; 52 53 public: 54 static char ID; // Pass identification, replacement for typeid 55 explicit SjLjEHPrepare() : FunctionPass(ID) {} 56 bool doInitialization(Module &M) override; 57 bool runOnFunction(Function &F) override; 58 59 void getAnalysisUsage(AnalysisUsage &AU) const override {} 60 StringRef getPassName() const override { 61 return "SJLJ Exception Handling preparation"; 62 } 63 64 private: 65 bool setupEntryBlockAndCallSites(Function &F); 66 void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal); 67 Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads); 68 void lowerIncomingArguments(Function &F); 69 void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes); 70 void insertCallSiteStore(Instruction *I, int Number); 71 }; 72 } // end anonymous namespace 73 74 char SjLjEHPrepare::ID = 0; 75 INITIALIZE_PASS(SjLjEHPrepare, DEBUG_TYPE, "Prepare SjLj exceptions", 76 false, false) 77 78 // Public Interface To the SjLjEHPrepare pass. 79 FunctionPass *llvm::createSjLjEHPreparePass() { return new SjLjEHPrepare(); } 80 // doInitialization - Set up decalarations and types needed to process 81 // exceptions. 82 bool SjLjEHPrepare::doInitialization(Module &M) { 83 // Build the function context structure. 84 // builtin_setjmp uses a five word jbuf 85 Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext()); 86 Type *Int32Ty = Type::getInt32Ty(M.getContext()); 87 doubleUnderDataTy = ArrayType::get(Int32Ty, 4); 88 doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5); 89 FunctionContextTy = StructType::get(VoidPtrTy, // __prev 90 Int32Ty, // call_site 91 doubleUnderDataTy, // __data 92 VoidPtrTy, // __personality 93 VoidPtrTy, // __lsda 94 doubleUnderJBufTy // __jbuf 95 ); 96 97 return true; 98 } 99 100 /// insertCallSiteStore - Insert a store of the call-site value to the 101 /// function context 102 void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) { 103 IRBuilder<> Builder(I); 104 105 // Get a reference to the call_site field. 106 Type *Int32Ty = Type::getInt32Ty(I->getContext()); 107 Value *Zero = ConstantInt::get(Int32Ty, 0); 108 Value *One = ConstantInt::get(Int32Ty, 1); 109 Value *Idxs[2] = { Zero, One }; 110 Value *CallSite = 111 Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site"); 112 113 // Insert a store of the call-site number 114 ConstantInt *CallSiteNoC = 115 ConstantInt::get(Type::getInt32Ty(I->getContext()), Number); 116 Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/); 117 } 118 119 /// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until 120 /// we reach blocks we've already seen. 121 static void MarkBlocksLiveIn(BasicBlock *BB, 122 SmallPtrSetImpl<BasicBlock *> &LiveBBs) { 123 if (!LiveBBs.insert(BB).second) 124 return; // already been here. 125 126 df_iterator_default_set<BasicBlock*> Visited; 127 128 for (BasicBlock *B : inverse_depth_first_ext(BB, Visited)) 129 LiveBBs.insert(B); 130 131 } 132 133 /// substituteLPadValues - Substitute the values returned by the landingpad 134 /// instruction with those returned by the personality function. 135 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, 136 Value *SelVal) { 137 SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end()); 138 while (!UseWorkList.empty()) { 139 Value *Val = UseWorkList.pop_back_val(); 140 auto *EVI = dyn_cast<ExtractValueInst>(Val); 141 if (!EVI) 142 continue; 143 if (EVI->getNumIndices() != 1) 144 continue; 145 if (*EVI->idx_begin() == 0) 146 EVI->replaceAllUsesWith(ExnVal); 147 else if (*EVI->idx_begin() == 1) 148 EVI->replaceAllUsesWith(SelVal); 149 if (EVI->use_empty()) 150 EVI->eraseFromParent(); 151 } 152 153 if (LPI->use_empty()) 154 return; 155 156 // There are still some uses of LPI. Construct an aggregate with the exception 157 // values and replace the LPI with that aggregate. 158 Type *LPadType = LPI->getType(); 159 Value *LPadVal = UndefValue::get(LPadType); 160 auto *SelI = cast<Instruction>(SelVal); 161 IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator())); 162 LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val"); 163 LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val"); 164 165 LPI->replaceAllUsesWith(LPadVal); 166 } 167 168 /// setupFunctionContext - Allocate the function context on the stack and fill 169 /// it with all of the data that we know at this point. 170 Value *SjLjEHPrepare::setupFunctionContext(Function &F, 171 ArrayRef<LandingPadInst *> LPads) { 172 BasicBlock *EntryBB = &F.front(); 173 174 // Create an alloca for the incoming jump buffer ptr and the new jump buffer 175 // that needs to be restored on all exits from the function. This is an alloca 176 // because the value needs to be added to the global context list. 177 auto &DL = F.getParent()->getDataLayout(); 178 unsigned Align = DL.getPrefTypeAlignment(FunctionContextTy); 179 FuncCtx = new AllocaInst(FunctionContextTy, DL.getAllocaAddrSpace(), 180 nullptr, Align, "fn_context", &EntryBB->front()); 181 182 // Fill in the function context structure. 183 for (LandingPadInst *LPI : LPads) { 184 IRBuilder<> Builder(LPI->getParent(), 185 LPI->getParent()->getFirstInsertionPt()); 186 187 // Reference the __data field. 188 Value *FCData = 189 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data"); 190 191 // The exception values come back in context->__data[0]. 192 Type *Int32Ty = Type::getInt32Ty(F.getContext()); 193 Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData, 194 0, 0, "exception_gep"); 195 Value *ExnVal = Builder.CreateLoad(Int32Ty, ExceptionAddr, true, "exn_val"); 196 ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy()); 197 198 Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData, 199 0, 1, "exn_selector_gep"); 200 Value *SelVal = 201 Builder.CreateLoad(Int32Ty, SelectorAddr, true, "exn_selector_val"); 202 203 substituteLPadValues(LPI, ExnVal, SelVal); 204 } 205 206 // Personality function 207 IRBuilder<> Builder(EntryBB->getTerminator()); 208 Value *PersonalityFn = F.getPersonalityFn(); 209 Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32( 210 FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep"); 211 Builder.CreateStore( 212 Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()), 213 PersonalityFieldPtr, /*isVolatile=*/true); 214 215 // LSDA address 216 Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr"); 217 Value *LSDAFieldPtr = 218 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep"); 219 Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true); 220 221 return FuncCtx; 222 } 223 224 /// lowerIncomingArguments - To avoid having to handle incoming arguments 225 /// specially, we lower each arg to a copy instruction in the entry block. This 226 /// ensures that the argument value itself cannot be live out of the entry 227 /// block. 228 void SjLjEHPrepare::lowerIncomingArguments(Function &F) { 229 BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin(); 230 while (isa<AllocaInst>(AfterAllocaInsPt) && 231 cast<AllocaInst>(AfterAllocaInsPt)->isStaticAlloca()) 232 ++AfterAllocaInsPt; 233 assert(AfterAllocaInsPt != F.front().end()); 234 235 for (auto &AI : F.args()) { 236 // Swift error really is a register that we model as memory -- instruction 237 // selection will perform mem-to-reg for us and spill/reload appropriately 238 // around calls that clobber it. There is no need to spill this 239 // value to the stack and doing so would not be allowed. 240 if (AI.isSwiftError()) 241 continue; 242 243 Type *Ty = AI.getType(); 244 245 // Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction. 246 Value *TrueValue = ConstantInt::getTrue(F.getContext()); 247 Value *UndefValue = UndefValue::get(Ty); 248 Instruction *SI = SelectInst::Create( 249 TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt); 250 AI.replaceAllUsesWith(SI); 251 252 // Reset the operand, because it was clobbered by the RAUW above. 253 SI->setOperand(1, &AI); 254 } 255 } 256 257 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind 258 /// edge and spill them. 259 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F, 260 ArrayRef<InvokeInst *> Invokes) { 261 // Finally, scan the code looking for instructions with bad live ranges. 262 for (BasicBlock &BB : F) { 263 for (Instruction &Inst : BB) { 264 // Ignore obvious cases we don't have to handle. In particular, most 265 // instructions either have no uses or only have a single use inside the 266 // current block. Ignore them quickly. 267 if (Inst.use_empty()) 268 continue; 269 if (Inst.hasOneUse() && 270 cast<Instruction>(Inst.user_back())->getParent() == &BB && 271 !isa<PHINode>(Inst.user_back())) 272 continue; 273 274 // If this is an alloca in the entry block, it's not a real register 275 // value. 276 if (auto *AI = dyn_cast<AllocaInst>(&Inst)) 277 if (AI->isStaticAlloca()) 278 continue; 279 280 // Avoid iterator invalidation by copying users to a temporary vector. 281 SmallVector<Instruction *, 16> Users; 282 for (User *U : Inst.users()) { 283 Instruction *UI = cast<Instruction>(U); 284 if (UI->getParent() != &BB || isa<PHINode>(UI)) 285 Users.push_back(UI); 286 } 287 288 // Find all of the blocks that this value is live in. 289 SmallPtrSet<BasicBlock *, 32> LiveBBs; 290 LiveBBs.insert(&BB); 291 while (!Users.empty()) { 292 Instruction *U = Users.pop_back_val(); 293 294 if (!isa<PHINode>(U)) { 295 MarkBlocksLiveIn(U->getParent(), LiveBBs); 296 } else { 297 // Uses for a PHI node occur in their predecessor block. 298 PHINode *PN = cast<PHINode>(U); 299 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 300 if (PN->getIncomingValue(i) == &Inst) 301 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs); 302 } 303 } 304 305 // Now that we know all of the blocks that this thing is live in, see if 306 // it includes any of the unwind locations. 307 bool NeedsSpill = false; 308 for (InvokeInst *Invoke : Invokes) { 309 BasicBlock *UnwindBlock = Invoke->getUnwindDest(); 310 if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) { 311 LLVM_DEBUG(dbgs() << "SJLJ Spill: " << Inst << " around " 312 << UnwindBlock->getName() << "\n"); 313 NeedsSpill = true; 314 break; 315 } 316 } 317 318 // If we decided we need a spill, do it. 319 // FIXME: Spilling this way is overkill, as it forces all uses of 320 // the value to be reloaded from the stack slot, even those that aren't 321 // in the unwind blocks. We should be more selective. 322 if (NeedsSpill) { 323 DemoteRegToStack(Inst, true); 324 ++NumSpilled; 325 } 326 } 327 } 328 329 // Go through the landing pads and remove any PHIs there. 330 for (InvokeInst *Invoke : Invokes) { 331 BasicBlock *UnwindBlock = Invoke->getUnwindDest(); 332 LandingPadInst *LPI = UnwindBlock->getLandingPadInst(); 333 334 // Place PHIs into a set to avoid invalidating the iterator. 335 SmallPtrSet<PHINode *, 8> PHIsToDemote; 336 for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN) 337 PHIsToDemote.insert(cast<PHINode>(PN)); 338 if (PHIsToDemote.empty()) 339 continue; 340 341 // Demote the PHIs to the stack. 342 for (PHINode *PN : PHIsToDemote) 343 DemotePHIToStack(PN); 344 345 // Move the landingpad instruction back to the top of the landing pad block. 346 LPI->moveBefore(&UnwindBlock->front()); 347 } 348 } 349 350 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling 351 /// the function context and marking the call sites with the appropriate 352 /// values. These values are used by the DWARF EH emitter. 353 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) { 354 SmallVector<ReturnInst *, 16> Returns; 355 SmallVector<InvokeInst *, 16> Invokes; 356 SmallSetVector<LandingPadInst *, 16> LPads; 357 358 // Look through the terminators of the basic blocks to find invokes. 359 for (BasicBlock &BB : F) 360 if (auto *II = dyn_cast<InvokeInst>(BB.getTerminator())) { 361 if (Function *Callee = II->getCalledFunction()) 362 if (Callee->getIntrinsicID() == Intrinsic::donothing) { 363 // Remove the NOP invoke. 364 BranchInst::Create(II->getNormalDest(), II); 365 II->eraseFromParent(); 366 continue; 367 } 368 369 Invokes.push_back(II); 370 LPads.insert(II->getUnwindDest()->getLandingPadInst()); 371 } else if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) { 372 Returns.push_back(RI); 373 } 374 375 if (Invokes.empty()) 376 return false; 377 378 NumInvokes += Invokes.size(); 379 380 lowerIncomingArguments(F); 381 lowerAcrossUnwindEdges(F, Invokes); 382 383 Value *FuncCtx = 384 setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end())); 385 BasicBlock *EntryBB = &F.front(); 386 IRBuilder<> Builder(EntryBB->getTerminator()); 387 388 // Get a reference to the jump buffer. 389 Value *JBufPtr = 390 Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep"); 391 392 // Save the frame pointer. 393 Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0, 394 "jbuf_fp_gep"); 395 396 Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp"); 397 Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true); 398 399 // Save the stack pointer. 400 Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2, 401 "jbuf_sp_gep"); 402 403 Val = Builder.CreateCall(StackAddrFn, {}, "sp"); 404 Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true); 405 406 // Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf. 407 Builder.CreateCall(BuiltinSetupDispatchFn, {}); 408 409 // Store a pointer to the function context so that the back-end will know 410 // where to look for it. 411 Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy()); 412 Builder.CreateCall(FuncCtxFn, FuncCtxArg); 413 414 // At this point, we are all set up, update the invoke instructions to mark 415 // their call_site values. 416 for (unsigned I = 0, E = Invokes.size(); I != E; ++I) { 417 insertCallSiteStore(Invokes[I], I + 1); 418 419 ConstantInt *CallSiteNum = 420 ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1); 421 422 // Record the call site value for the back end so it stays associated with 423 // the invoke. 424 CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]); 425 } 426 427 // Mark call instructions that aren't nounwind as no-action (call_site == 428 // -1). Skip the entry block, as prior to then, no function context has been 429 // created for this function and any unexpected exceptions thrown will go 430 // directly to the caller's context, which is what we want anyway, so no need 431 // to do anything here. 432 for (BasicBlock &BB : F) { 433 if (&BB == &F.front()) 434 continue; 435 for (Instruction &I : BB) 436 if (I.mayThrow()) 437 insertCallSiteStore(&I, -1); 438 } 439 440 // Register the function context and make sure it's known to not throw 441 CallInst *Register = 442 CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator()); 443 Register->setDoesNotThrow(); 444 445 // Following any allocas not in the entry block, update the saved SP in the 446 // jmpbuf to the new value. 447 for (BasicBlock &BB : F) { 448 if (&BB == &F.front()) 449 continue; 450 for (Instruction &I : BB) { 451 if (auto *CI = dyn_cast<CallInst>(&I)) { 452 if (CI->getCalledFunction() != StackRestoreFn) 453 continue; 454 } else if (!isa<AllocaInst>(&I)) { 455 continue; 456 } 457 Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp"); 458 StackAddr->insertAfter(&I); 459 Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true); 460 StoreStackAddr->insertAfter(StackAddr); 461 } 462 } 463 464 // Finally, for any returns from this function, if this function contains an 465 // invoke, add a call to unregister the function context. 466 for (ReturnInst *Return : Returns) 467 CallInst::Create(UnregisterFn, FuncCtx, "", Return); 468 469 return true; 470 } 471 472 bool SjLjEHPrepare::runOnFunction(Function &F) { 473 Module &M = *F.getParent(); 474 RegisterFn = M.getOrInsertFunction( 475 "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()), 476 PointerType::getUnqual(FunctionContextTy)); 477 UnregisterFn = M.getOrInsertFunction( 478 "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()), 479 PointerType::getUnqual(FunctionContextTy)); 480 FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress); 481 StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave); 482 StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore); 483 BuiltinSetupDispatchFn = 484 Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch); 485 LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda); 486 CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite); 487 FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext); 488 489 bool Res = setupEntryBlockAndCallSites(F); 490 return Res; 491 } 492