| //===-- X86WinEHUnwindV2.cpp - Win x64 Unwind v2 ----------------*- C++ -*-===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| /// |
| /// Implements the analysis required to detect if a function can use Unwind v2 |
| /// information, and emits the neccesary pseudo instructions used by MC to |
| /// generate the unwind info. |
| /// |
| //===----------------------------------------------------------------------===// |
| |
| #include "MCTargetDesc/X86BaseInfo.h" |
| #include "X86.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/CodeGen/MachineBasicBlock.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/TargetFrameLowering.h" |
| #include "llvm/CodeGen/TargetInstrInfo.h" |
| #include "llvm/CodeGen/TargetSubtargetInfo.h" |
| #include "llvm/IR/DiagnosticInfo.h" |
| #include "llvm/IR/Module.h" |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "x86-wineh-unwindv2" |
| |
| STATISTIC(MeetsUnwindV2Criteria, |
| "Number of functions that meet Unwind v2 criteria"); |
| STATISTIC(FailsUnwindV2Criteria, |
| "Number of functions that fail Unwind v2 criteria"); |
| |
| static cl::opt<unsigned> |
| UnwindCodeThreshold("x86-wineh-unwindv2-unwind-codes-threshold", cl::Hidden, |
| cl::desc("Maximum number of unwind codes before " |
| "splitting into a new unwind info."), |
| cl::init(UINT8_MAX)); |
| |
| static cl::opt<unsigned> |
| ForceMode("x86-wineh-unwindv2-force-mode", cl::Hidden, |
| cl::desc("Overwrites the Unwind v2 mode for testing purposes.")); |
| |
| // This threshold is for the *approximate* number of instructions, see the |
| // comment in runAnalysisOnFuncOrFunclet for more details. |
| static cl::opt<unsigned> InstructionCountThreshold( |
| "x86-wineh-unwindv2-instruction-count-threshold", cl::Hidden, |
| cl::desc("Maximum number of (approximate) instructions before splitting " |
| "into a new unwind info."), |
| cl::init(600)); |
| |
| namespace { |
| |
| struct EpilogInfo { |
| MachineInstr *UnwindV2StartLocation; |
| unsigned ApproximateInstructionPosition; |
| }; |
| |
| struct FrameInfo { |
| unsigned ApproximatePrologCodeCount; |
| unsigned ApproximateInstructionCount; |
| SmallVector<EpilogInfo> EpilogInfos; |
| }; |
| |
| class X86WinEHUnwindV2 : public MachineFunctionPass { |
| public: |
| static char ID; |
| |
| X86WinEHUnwindV2() : MachineFunctionPass(ID) { |
| initializeX86WinEHUnwindV2Pass(*PassRegistry::getPassRegistry()); |
| } |
| |
| StringRef getPassName() const override { return "WinEH Unwind V2"; } |
| |
| bool runOnMachineFunction(MachineFunction &MF) override; |
| |
| private: |
| /// Rejects the current function due to an internal error within LLVM. |
| static std::nullopt_t rejectCurrentFunctionInternalError( |
| const MachineFunction &MF, WinX64EHUnwindV2Mode Mode, StringRef Reason); |
| |
| // Continues running the analysis on the given function or funclet. |
| static std::optional<FrameInfo> |
| runAnalysisOnFuncOrFunclet(MachineFunction &MF, |
| MachineFunction::iterator &Iter, |
| WinX64EHUnwindV2Mode Mode); |
| }; |
| |
| enum class FunctionState { |
| InProlog, |
| HasProlog, |
| InEpilog, |
| FinishedEpilog, |
| }; |
| |
| } // end anonymous namespace |
| |
| char X86WinEHUnwindV2::ID = 0; |
| |
| INITIALIZE_PASS(X86WinEHUnwindV2, "x86-wineh-unwindv2", |
| "Analyze and emit instructions for Win64 Unwind v2", false, |
| false) |
| |
| FunctionPass *llvm::createX86WinEHUnwindV2Pass() { |
| return new X86WinEHUnwindV2(); |
| } |
| |
| DebugLoc findDebugLoc(const MachineBasicBlock &MBB) { |
| for (const MachineInstr &MI : MBB) |
| if (MI.getDebugLoc()) |
| return MI.getDebugLoc(); |
| |
| return DebugLoc::getUnknown(); |
| } |
| |
| std::optional<FrameInfo> |
| X86WinEHUnwindV2::runAnalysisOnFuncOrFunclet(MachineFunction &MF, |
| MachineFunction::iterator &Iter, |
| WinX64EHUnwindV2Mode Mode) { |
| const TargetFrameLowering &TFL = *MF.getSubtarget().getFrameLowering(); |
| |
| // Current state of processing the function. We'll assume that all functions |
| // start with a prolog. |
| FunctionState State = FunctionState::InProlog; |
| |
| // Prolog information. |
| SmallVector<int64_t> PushedRegs; |
| bool HasStackAlloc = false; |
| bool HasSetFrame = false; |
| unsigned ApproximatePrologCodeCount = 0; |
| |
| SmallVector<EpilogInfo> EpilogInfos; |
| |
| // Unwind v2 requires that the epilog is no more than 4Kb away from the last |
| // instruction that the current unwind info covers. If we believe that we are |
| // going over that limit then we need to split the unwind info. Ideally we'd |
| // do this at the point where we actually know how far away we are from the |
| // last instruction, but that's not possible here and splitting unwind infos |
| // in MC would be difficult. However, the cost of splitting an unwind info is |
| // fairly cheap (in the other of bytes in the xdata section), so we can |
| // instead use a heuristic based on the number of MachineInstrs to decide when |
| // to split unwind infos, and allow users to tune the threshold if needed. |
| // This is not a perfect solution, but 1) it is cheap to calculate, 2) allows |
| // the common case for small functions or large functions with multiple |
| // returns at the end to have a single unwind info, and 3) allows unwind v2 to |
| // be used in large functions (that would otherwise be rejected) for a small |
| // binary size cost. |
| unsigned ApproximateInstructionCount = 0; |
| |
| for (; Iter != MF.end(); ++Iter) { |
| MachineBasicBlock &MBB = *Iter; |
| |
| // If we're already been processing a function, then come across a funclet |
| // then break since the funclet will get a fresh frame info. |
| if (MBB.isEHFuncletEntry() && State != FunctionState::InProlog) |
| break; |
| |
| // Current epilog information. We assume that epilogs cannot cross basic |
| // block boundaries. |
| unsigned PoppedRegCount = 0; |
| bool HasStackDealloc = false; |
| bool HasSetFrameBack = false; |
| MachineInstr *UnwindV2StartLocation = nullptr; |
| |
| for (MachineInstr &MI : MBB) { |
| // This is an *approximation* of the number of instructions that will be |
| // emitted. It is not the actual number of instructions, but that doesn't |
| // matter: see the comment at the declaration of |
| // ApproximateInstructionCount. |
| if (!MI.isPseudo() && !MI.isMetaInstruction()) |
| ApproximateInstructionCount++; |
| |
| switch (MI.getOpcode()) { |
| // |
| // Prolog handling. |
| // |
| case X86::SEH_PushReg: |
| if (State != FunctionState::InProlog) |
| llvm_unreachable("SEH_PushReg outside of prolog"); |
| ApproximatePrologCodeCount++; |
| PushedRegs.push_back(MI.getOperand(0).getImm()); |
| break; |
| |
| case X86::SEH_StackAlloc: |
| if (State != FunctionState::InProlog) |
| llvm_unreachable("SEH_StackAlloc outside of prolog"); |
| // Assume a large alloc... |
| ApproximatePrologCodeCount += 3; |
| HasStackAlloc = true; |
| break; |
| |
| case X86::SEH_SetFrame: |
| if (State != FunctionState::InProlog) |
| llvm_unreachable("SEH_SetFrame outside of prolog"); |
| ApproximatePrologCodeCount++; |
| HasSetFrame = true; |
| break; |
| |
| case X86::SEH_SaveReg: |
| case X86::SEH_SaveXMM: |
| if (State != FunctionState::InProlog) |
| llvm_unreachable("SEH_SaveXMM or SEH_SaveReg outside of prolog"); |
| // Assume a big reg... |
| ApproximatePrologCodeCount += 3; |
| break; |
| |
| case X86::SEH_PushFrame: |
| if (State != FunctionState::InProlog) |
| llvm_unreachable("SEH_PushFrame outside of prolog"); |
| ApproximatePrologCodeCount++; |
| break; |
| |
| case X86::SEH_EndPrologue: |
| if (State != FunctionState::InProlog) |
| llvm_unreachable("SEH_EndPrologue outside of prolog"); |
| State = FunctionState::HasProlog; |
| break; |
| |
| // |
| // Epilog handling. |
| // |
| case X86::SEH_BeginEpilogue: |
| if (State != FunctionState::HasProlog) |
| llvm_unreachable("SEH_BeginEpilogue in prolog or another epilog"); |
| State = FunctionState::InEpilog; |
| break; |
| |
| case X86::SEH_EndEpilogue: |
| if (State != FunctionState::InEpilog) |
| llvm_unreachable("SEH_EndEpilogue outside of epilog"); |
| if (HasStackAlloc != HasStackDealloc) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "The prolog made a stack allocation, " |
| "but the epilog did not deallocate it"); |
| if (PoppedRegCount != PushedRegs.size()) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "The prolog pushed more registers than " |
| "the epilog popped"); |
| |
| // If we didn't find the start location, then use the end of the |
| // epilog. |
| if (!UnwindV2StartLocation) |
| UnwindV2StartLocation = &MI; |
| EpilogInfos.push_back( |
| {UnwindV2StartLocation, ApproximateInstructionCount}); |
| State = FunctionState::FinishedEpilog; |
| break; |
| |
| case X86::MOV64rr: |
| if (State == FunctionState::InEpilog) { |
| // If the prolog contains a stack allocation, then the first |
| // instruction in the epilog must be to adjust the stack pointer. |
| if (!HasSetFrame) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "The epilog is setting frame back, but prolog did not set it"); |
| if (PoppedRegCount > 0) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "The epilog is setting the frame back after popping " |
| "registers"); |
| if (HasStackDealloc) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "Cannot set the frame back after the stack " |
| "allocation has been deallocated"); |
| HasSetFrameBack = true; |
| } else if (State == FunctionState::FinishedEpilog) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, "Unexpected mov instruction after the epilog"); |
| break; |
| |
| case X86::LEA64r: |
| case X86::ADD64ri32: |
| if (State == FunctionState::InEpilog) { |
| // If the prolog contains a stack allocation, then the first |
| // instruction in the epilog must be to adjust the stack pointer. |
| if (!HasStackAlloc) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "The epilog is deallocating a stack " |
| "allocation, but the prolog did " |
| "not allocate one"); |
| if (PoppedRegCount > 0) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "The epilog is deallocating a stack allocation after popping " |
| "registers"); |
| |
| HasStackDealloc = true; |
| } else if (State == FunctionState::FinishedEpilog) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, "Unexpected lea or add instruction after the epilog"); |
| break; |
| |
| case X86::POP64r: |
| if (State == FunctionState::InEpilog) { |
| Register Reg = MI.getOperand(0).getReg(); |
| if (HasStackAlloc && (PoppedRegCount == 0) && |
| !llvm::is_contained(PushedRegs, Reg)) { |
| // If this is a pop that doesn't correspond to the set of pushed |
| // registers, then assume it was used to adjust the stack pointer. |
| HasStackDealloc = true; |
| } else { |
| // Special case: no explicit stack dealloc is required if SetFrame |
| // was used and the function has a frame pointer. |
| if (PoppedRegCount == 0 && HasStackAlloc && !HasStackDealloc && |
| HasSetFrameBack && TFL.hasFP(MF)) |
| HasStackDealloc = true; |
| |
| // After the stack pointer has been adjusted, the epilog must |
| // POP each register in reverse order of the PUSHes in the prolog. |
| PoppedRegCount++; |
| if (HasStackAlloc != HasStackDealloc) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "Cannot pop registers before the stack " |
| "allocation has been deallocated"); |
| if (PoppedRegCount > PushedRegs.size()) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "The epilog is popping more registers than the prolog " |
| "pushed"); |
| if (PushedRegs[PushedRegs.size() - PoppedRegCount] != Reg.id()) |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, |
| "The epilog is popping a registers in " |
| "a different order than the " |
| "prolog pushed them"); |
| |
| // Unwind v2 records the size of the epilog not from where we place |
| // SEH_BeginEpilogue (as that contains the instruction to adjust the |
| // stack pointer) but from the first POP instruction (if there is |
| // one). |
| if (!UnwindV2StartLocation) { |
| assert(PoppedRegCount == 1); |
| UnwindV2StartLocation = &MI; |
| } |
| } |
| } else if (State == FunctionState::FinishedEpilog) |
| // Unexpected instruction after the epilog. |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, "Registers are being popped after the epilog"); |
| break; |
| |
| default: |
| if (MI.isTerminator()) { |
| if (State == FunctionState::FinishedEpilog) |
| // Found the terminator after the epilog, we're now ready for |
| // another epilog. |
| State = FunctionState::HasProlog; |
| else if (State == FunctionState::InEpilog) |
| llvm_unreachable("Terminator in the middle of the epilog"); |
| } else if (!MI.isDebugOrPseudoInstr()) { |
| if ((State == FunctionState::FinishedEpilog) || |
| (State == FunctionState::InEpilog)) |
| // Unknown instruction in or after the epilog. |
| return rejectCurrentFunctionInternalError( |
| MF, Mode, "Unexpected instruction in or after the epilog"); |
| } |
| } |
| } |
| } |
| |
| return FrameInfo{ApproximatePrologCodeCount, ApproximateInstructionCount, |
| EpilogInfos}; |
| } |
| |
| bool X86WinEHUnwindV2::runOnMachineFunction(MachineFunction &MF) { |
| WinX64EHUnwindV2Mode Mode = |
| ForceMode.getNumOccurrences() |
| ? static_cast<WinX64EHUnwindV2Mode>(ForceMode.getValue()) |
| : MF.getFunction().getParent()->getWinX64EHUnwindV2Mode(); |
| |
| if (Mode == WinX64EHUnwindV2Mode::Disabled) |
| return false; |
| |
| // Requested changes. |
| SmallVector<FrameInfo> FrameInfos; |
| MachineFunction::iterator Iter = MF.begin(); |
| while (Iter != MF.end()) { |
| auto FI = runAnalysisOnFuncOrFunclet(MF, Iter, Mode); |
| if (!FI) |
| return false; |
| if (!FI->EpilogInfos.empty()) |
| FrameInfos.push_back(std::move(*FI)); |
| } |
| |
| if (FrameInfos.empty()) |
| return false; |
| |
| MeetsUnwindV2Criteria++; |
| |
| const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo(); |
| for (auto &FI : FrameInfos) { |
| // Walk the list of epilogs backwards and add new SEH pseudo instructions: |
| // * SEH_UnwindV2Start at the start of each epilog. |
| // * If the current instruction is too far away from where the last unwind |
| // info ended OR there are too many unwind codes in the info, then add |
| // SEH_SplitChainedAtEndOfBlock to finish the current info. |
| unsigned LastUnwindInfoEndPosition = FI.ApproximateInstructionCount; |
| unsigned UnwindCodeCount = FI.ApproximatePrologCodeCount + 1; |
| for (auto &Info : llvm::reverse(FI.EpilogInfos)) { |
| MachineBasicBlock &MBB = *Info.UnwindV2StartLocation->getParent(); |
| const DebugLoc &DL = Info.UnwindV2StartLocation->getDebugLoc(); |
| BuildMI(MBB, Info.UnwindV2StartLocation, DL, |
| TII->get(X86::SEH_UnwindV2Start)); |
| |
| if ((LastUnwindInfoEndPosition - Info.ApproximateInstructionPosition >= |
| InstructionCountThreshold) || |
| (UnwindCodeCount >= UnwindCodeThreshold)) { |
| BuildMI(MBB, MBB.begin(), DL, |
| TII->get(X86::SEH_SplitChainedAtEndOfBlock)); |
| LastUnwindInfoEndPosition = Info.ApproximateInstructionPosition; |
| // Doesn't reset to 0, as the prolog unwind codes are now in this info. |
| UnwindCodeCount = FI.ApproximatePrologCodeCount + 1; |
| } |
| |
| UnwindCodeCount++; |
| } |
| } |
| |
| // Note that the function is using Unwind v2. |
| MachineBasicBlock &FirstMBB = MF.front(); |
| BuildMI(FirstMBB, FirstMBB.front(), findDebugLoc(FirstMBB), |
| TII->get(X86::SEH_UnwindVersion)) |
| .addImm(2); |
| |
| return true; |
| } |
| |
| std::nullopt_t X86WinEHUnwindV2::rejectCurrentFunctionInternalError( |
| const MachineFunction &MF, WinX64EHUnwindV2Mode Mode, StringRef Reason) { |
| if (Mode == WinX64EHUnwindV2Mode::Required) |
| reportFatalInternalError("Windows x64 Unwind v2 is required, but LLVM has " |
| "generated incompatible code in function '" + |
| MF.getName() + "': " + Reason); |
| |
| FailsUnwindV2Criteria++; |
| return std::nullopt; |
| } |
