| //===----- X86AvoidTrailingCall.cpp - Insert int3 after trailing calls ----===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // The Windows x64 unwinder has trouble unwinding the stack when a return |
| // address points to the end of the function. This pass maintains the invariant |
| // that every return address is inside the bounds of its parent function or |
| // funclet by inserting int3 if the last instruction would otherwise be a call. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "X86.h" |
| #include "X86InstrInfo.h" |
| #include "X86Subtarget.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| |
| #define DEBUG_TYPE "x86-avoid-trailing-call" |
| |
| using namespace llvm; |
| |
| namespace { |
| |
| class X86AvoidTrailingCallPass : public MachineFunctionPass { |
| public: |
| X86AvoidTrailingCallPass() : MachineFunctionPass(ID) {} |
| |
| bool runOnMachineFunction(MachineFunction &MF) override; |
| |
| private: |
| StringRef getPassName() const override { |
| return "X86 avoid trailing call pass"; |
| } |
| static char ID; |
| }; |
| |
| char X86AvoidTrailingCallPass::ID = 0; |
| |
| } // end anonymous namespace |
| |
| FunctionPass *llvm::createX86AvoidTrailingCallPass() { |
| return new X86AvoidTrailingCallPass(); |
| } |
| |
| // A real instruction is a non-meta, non-pseudo instruction. Some pseudos |
| // expand to nothing, and some expand to code. This logic conservatively assumes |
| // they might expand to nothing. |
| static bool isRealInstruction(MachineInstr &MI) { |
| return !MI.isPseudo() && !MI.isMetaInstruction(); |
| } |
| |
| // Return true if this is a call instruction, but not a tail call. |
| static bool isCallInstruction(const MachineInstr &MI) { |
| return MI.isCall() && !MI.isReturn(); |
| } |
| |
| bool X86AvoidTrailingCallPass::runOnMachineFunction(MachineFunction &MF) { |
| const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>(); |
| const X86InstrInfo &TII = *STI.getInstrInfo(); |
| assert(STI.isTargetWin64() && "pass only runs on Win64"); |
| |
| // FIXME: Perhaps this pass should also replace SEH_Epilogue by inserting nops |
| // before epilogues. |
| |
| bool Changed = false; |
| for (MachineBasicBlock &MBB : MF) { |
| // Look for basic blocks that precede funclet entries or are at the end of |
| // the function. |
| MachineBasicBlock *NextMBB = MBB.getNextNode(); |
| if (NextMBB && !NextMBB->isEHFuncletEntry()) |
| continue; |
| |
| // Find the last real instruction in this block, or previous blocks if this |
| // block is empty. |
| MachineBasicBlock::reverse_iterator LastRealInstr; |
| for (MachineBasicBlock &RMBB : |
| make_range(MBB.getReverseIterator(), MF.rend())) { |
| LastRealInstr = llvm::find_if(reverse(RMBB), isRealInstruction); |
| if (LastRealInstr != RMBB.rend()) |
| break; |
| } |
| |
| // Do nothing if this function or funclet has no instructions. |
| if (LastRealInstr == MF.begin()->rend()) |
| continue; |
| |
| // If this is a call instruction, insert int3 right after it with the same |
| // DebugLoc. Convert back to a forward iterator and advance the insertion |
| // position once. |
| if (isCallInstruction(*LastRealInstr)) { |
| LLVM_DEBUG({ |
| dbgs() << "inserting int3 after trailing call instruction:\n"; |
| LastRealInstr->dump(); |
| dbgs() << '\n'; |
| }); |
| |
| MachineBasicBlock::iterator MBBI = std::next(LastRealInstr.getReverse()); |
| BuildMI(*LastRealInstr->getParent(), MBBI, LastRealInstr->getDebugLoc(), |
| TII.get(X86::INT3)); |
| Changed = true; |
| } |
| } |
| |
| return Changed; |
| } |