AArch64Arm64ECCallLowering.cpp

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//===-- AArch64Arm64ECCallLowering.cpp - Lower Arm64EC calls ----*- 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
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file contains the IR transform to lower external or indirect calls for
/// the ARM64EC calling convention. Such calls must go through the runtime, so
/// we can translate the calling convention for calls into the emulator.
///
/// This subsumes Control Flow Guard handling.
///
//===----------------------------------------------------------------------===//
 
#include "AArch64.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Mangler.h"
#include "llvm/IR/Module.h"
#include "llvm/Object/COFF.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/TargetParser/Triple.h"
 
using namespace llvm;
using namespace llvm::COFF;
 
using OperandBundleDef = OperandBundleDefT<Value *>;
 
#define DEBUG_TYPE "arm64eccalllowering"
 
STATISTIC(Arm64ECCallsLowered, "Number of Arm64EC calls lowered");
 
static cl::opt<bool> LowerDirectToIndirect("arm64ec-lower-direct-to-indirect",
                                           cl::Hidden, cl::init(true));
static cl::opt<bool> GenerateThunks("arm64ec-generate-thunks", cl::Hidden,
                                    cl::init(true));
 
namespace {
 
enum ThunkArgTranslation : uint8_t {
  Direct,
  Bitcast,
  PointerIndirection,
};
 
struct ThunkArgInfo {
  Type *Arm64Ty;
  Type *X64Ty;
  ThunkArgTranslation Translation;
};
 
class AArch64Arm64ECCallLowering : public ModulePass {
public:
  static char ID;
  AArch64Arm64ECCallLowering() : ModulePass(ID) {}
 
  Function *buildExitThunk(FunctionType *FnTy, AttributeList Attrs);
  Function *buildEntryThunk(Function *F);
  void lowerCall(CallBase *CB);
  Function *buildGuestExitThunk(Function *F);
  Function *buildPatchableThunk(GlobalAlias *UnmangledAlias,
                                GlobalAlias *MangledAlias);
  bool processFunction(Function &F, SetVector<GlobalValue *> &DirectCalledFns,
                       DenseMap<GlobalAlias *, GlobalAlias *> &FnsMap);
  bool runOnModule(Module &M) override;
 
private:
  ControlFlowGuardMode CFGuardModuleFlag = ControlFlowGuardMode::Disabled;
  FunctionType *GuardFnType = nullptr;
  FunctionType *DispatchFnType = nullptr;
  Constant *GuardFnCFGlobal = nullptr;
  Constant *GuardFnGlobal = nullptr;
  Constant *DispatchFnGlobal = nullptr;
  Module *M = nullptr;
 
  Type *PtrTy;
  Type *I64Ty;
  Type *VoidTy;
 
  void getThunkType(FunctionType *FT, AttributeList AttrList,
                    Arm64ECThunkType TT, raw_ostream &Out,
                    FunctionType *&Arm64Ty, FunctionType *&X64Ty,
                    SmallVector<ThunkArgTranslation> &ArgTranslations);
  void getThunkRetType(FunctionType *FT, AttributeList AttrList,
                       raw_ostream &Out, Type *&Arm64RetTy, Type *&X64RetTy,
                       SmallVectorImpl<Type *> &Arm64ArgTypes,
                       SmallVectorImpl<Type *> &X64ArgTypes,
                       SmallVector<ThunkArgTranslation> &ArgTranslations,
                       bool &HasSretPtr);
  void getThunkArgTypes(FunctionType *FT, AttributeList AttrList,
                        Arm64ECThunkType TT, raw_ostream &Out,
                        SmallVectorImpl<Type *> &Arm64ArgTypes,
                        SmallVectorImpl<Type *> &X64ArgTypes,
                        SmallVectorImpl<ThunkArgTranslation> &ArgTranslations,
                        bool HasSretPtr);
  ThunkArgInfo canonicalizeThunkType(Type *T, Align Alignment, bool Ret,
                                     uint64_t ArgSizeBytes, raw_ostream &Out);
};
 
} // end anonymous namespace
 
void AArch64Arm64ECCallLowering::getThunkType(
    FunctionType *FT, AttributeList AttrList, Arm64ECThunkType TT,
    raw_ostream &Out, FunctionType *&Arm64Ty, FunctionType *&X64Ty,
    SmallVector<ThunkArgTranslation> &ArgTranslations) {
  Out << (TT == Arm64ECThunkType::Entry ? "$ientry_thunk$cdecl$"
                                        : "$iexit_thunk$cdecl$");
 
  Type *Arm64RetTy;
  Type *X64RetTy;
 
  SmallVector<Type *> Arm64ArgTypes;
  SmallVector<Type *> X64ArgTypes;
 
  // The first argument to a thunk is the called function, stored in x9.
  // For exit thunks, we pass the called function down to the emulator;
  // for entry/guest exit thunks, we just call the Arm64 function directly.
  if (TT == Arm64ECThunkType::Exit)
    Arm64ArgTypes.push_back(PtrTy);
  X64ArgTypes.push_back(PtrTy);
 
  bool HasSretPtr = false;
  getThunkRetType(FT, AttrList, Out, Arm64RetTy, X64RetTy, Arm64ArgTypes,
                  X64ArgTypes, ArgTranslations, HasSretPtr);
 
  getThunkArgTypes(FT, AttrList, TT, Out, Arm64ArgTypes, X64ArgTypes,
                   ArgTranslations, HasSretPtr);
 
  Arm64Ty = FunctionType::get(Arm64RetTy, Arm64ArgTypes, false);
 
  X64Ty = FunctionType::get(X64RetTy, X64ArgTypes, false);
}
 
void AArch64Arm64ECCallLowering::getThunkArgTypes(
    FunctionType *FT, AttributeList AttrList, Arm64ECThunkType TT,
    raw_ostream &Out, SmallVectorImpl<Type *> &Arm64ArgTypes,
    SmallVectorImpl<Type *> &X64ArgTypes,
    SmallVectorImpl<ThunkArgTranslation> &ArgTranslations, bool HasSretPtr) {
 
  Out << "$";
  if (FT->isVarArg()) {
    // We treat the variadic function's thunk as a normal function
    // with the following type on the ARM side:
    //   rettype exitthunk(
    //     ptr x9, ptr x0, i64 x1, i64 x2, i64 x3, ptr x4, i64 x5)
    //
    // that can coverage all types of variadic function.
    // x9 is similar to normal exit thunk, store the called function.
    // x0-x3 is the arguments be stored in registers.
    // x4 is the address of the arguments on the stack.
    // x5 is the size of the arguments on the stack.
    //
    // On the x64 side, it's the same except that x5 isn't set.
    //
    // If both the ARM and X64 sides are sret, there are only three
    // arguments in registers.
    //
    // If the X64 side is sret, but the ARM side isn't, we pass an extra value
    // to/from the X64 side, and let SelectionDAG transform it into a memory
    // location.
    Out << "varargs";
 
    // x0-x3
    for (int i = HasSretPtr ? 1 : 0; i < 4; i++) {
      Arm64ArgTypes.push_back(I64Ty);
      X64ArgTypes.push_back(I64Ty);
      ArgTranslations.push_back(ThunkArgTranslation::Direct);
    }
 
    // x4
    Arm64ArgTypes.push_back(PtrTy);
    X64ArgTypes.push_back(PtrTy);
    ArgTranslations.push_back(ThunkArgTranslation::Direct);
    // x5
    Arm64ArgTypes.push_back(I64Ty);
    if (TT != Arm64ECThunkType::Entry) {
      // FIXME: x5 isn't actually used by the x64 side; revisit once we
      // have proper isel for varargs
      X64ArgTypes.push_back(I64Ty);
      ArgTranslations.push_back(ThunkArgTranslation::Direct);
    }
    return;
  }
 
  unsigned I = 0;
  if (HasSretPtr)
    I++;
 
  if (I == FT->getNumParams()) {
    Out << "v";
    return;
  }
 
  for (unsigned E = FT->getNumParams(); I != E; ++I) {
#if 0
    // FIXME: Need more information about argument size; see
    // https://reviews.llvm.org/D132926
    uint64_t ArgSizeBytes = AttrList.getParamArm64ECArgSizeBytes(I);
    Align ParamAlign = AttrList.getParamAlignment(I).valueOrOne();
#else
    uint64_t ArgSizeBytes = 0;
    Align ParamAlign = Align();
#endif
    auto [Arm64Ty, X64Ty, ArgTranslation] =
        canonicalizeThunkType(FT->getParamType(I), ParamAlign,
                              /*Ret*/ false, ArgSizeBytes, Out);
    Arm64ArgTypes.push_back(Arm64Ty);
    X64ArgTypes.push_back(X64Ty);
    ArgTranslations.push_back(ArgTranslation);
  }
}
 
void AArch64Arm64ECCallLowering::getThunkRetType(
    FunctionType *FT, AttributeList AttrList, raw_ostream &Out,
    Type *&Arm64RetTy, Type *&X64RetTy, SmallVectorImpl<Type *> &Arm64ArgTypes,
    SmallVectorImpl<Type *> &X64ArgTypes,
    SmallVector<ThunkArgTranslation> &ArgTranslations, bool &HasSretPtr) {
  Type *T = FT->getReturnType();
#if 0
  // FIXME: Need more information about argument size; see
  // https://reviews.llvm.org/D132926
  uint64_t ArgSizeBytes = AttrList.getRetArm64ECArgSizeBytes();
#else
  int64_t ArgSizeBytes = 0;
#endif
  if (T->isVoidTy()) {
    if (FT->getNumParams()) {
      Attribute SRetAttr0 = AttrList.getParamAttr(0, Attribute::StructRet);
      Attribute InRegAttr0 = AttrList.getParamAttr(0, Attribute::InReg);
      Attribute SRetAttr1, InRegAttr1;
      if (FT->getNumParams() > 1) {
        // Also check the second parameter (for class methods, the first
        // parameter is "this", and the second parameter is the sret pointer.)
        // It doesn't matter which one is sret.
        SRetAttr1 = AttrList.getParamAttr(1, Attribute::StructRet);
        InRegAttr1 = AttrList.getParamAttr(1, Attribute::InReg);
      }
      if ((SRetAttr0.isValid() && InRegAttr0.isValid()) ||
          (SRetAttr1.isValid() && InRegAttr1.isValid())) {
        // sret+inreg indicates a call that returns a C++ class value. This is
        // actually equivalent to just passing and returning a void* pointer
        // as the first or second argument. Translate it that way, instead of
        // trying to model "inreg" in the thunk's calling convention; this
        // simplfies the rest of the code, and matches MSVC mangling.
        Out << "i8";
        Arm64RetTy = I64Ty;
        X64RetTy = I64Ty;
        return;
      }
      if (SRetAttr0.isValid()) {
        // FIXME: Sanity-check the sret type; if it's an integer or pointer,
        // we'll get screwy mangling/codegen.
        // FIXME: For large struct types, mangle as an integer argument and
        // integer return, so we can reuse more thunks, instead of "m" syntax.
        // (MSVC mangles this case as an integer return with no argument, but
        // that's a miscompile.)
        Type *SRetType = SRetAttr0.getValueAsType();
        Align SRetAlign = AttrList.getParamAlignment(0).valueOrOne();
        canonicalizeThunkType(SRetType, SRetAlign, /*Ret*/ true, ArgSizeBytes,
                              Out);
        Arm64RetTy = VoidTy;
        X64RetTy = VoidTy;
        Arm64ArgTypes.push_back(FT->getParamType(0));
        X64ArgTypes.push_back(FT->getParamType(0));
        ArgTranslations.push_back(ThunkArgTranslation::Direct);
        HasSretPtr = true;
        return;
      }
    }
 
    Out << "v";
    Arm64RetTy = VoidTy;
    X64RetTy = VoidTy;
    return;
  }
 
  auto info =
      canonicalizeThunkType(T, Align(), /*Ret*/ true, ArgSizeBytes, Out);
  Arm64RetTy = info.Arm64Ty;
  X64RetTy = info.X64Ty;
  if (X64RetTy->isPointerTy()) {
    // If the X64 type is canonicalized to a pointer, that means it's
    // passed/returned indirectly. For a return value, that means it's an
    // sret pointer.
    X64ArgTypes.push_back(X64RetTy);
    X64RetTy = VoidTy;
  }
}
 
ThunkArgInfo AArch64Arm64ECCallLowering::canonicalizeThunkType(
    Type *T, Align Alignment, bool Ret, uint64_t ArgSizeBytes,
    raw_ostream &Out) {
 
  auto direct = [](Type *T) {
    return ThunkArgInfo{T, T, ThunkArgTranslation::Direct};
  };
 
  auto bitcast = [this](Type *Arm64Ty, uint64_t SizeInBytes) {
    return ThunkArgInfo{Arm64Ty,
                        llvm::Type::getIntNTy(M->getContext(), SizeInBytes * 8),
                        ThunkArgTranslation::Bitcast};
  };
 
  auto pointerIndirection = [this](Type *Arm64Ty) {
    return ThunkArgInfo{Arm64Ty, PtrTy,
                        ThunkArgTranslation::PointerIndirection};
  };
 
  if (T->isHalfTy()) {
    // Prefix with `llvm` since MSVC doesn't specify `_Float16`
    Out << "__llvm_h__";
    return direct(T);
  }
 
  if (T->isFloatTy()) {
    Out << "f";
    return direct(T);
  }
 
  if (T->isDoubleTy()) {
    Out << "d";
    return direct(T);
  }
 
  if (T->isFloatingPointTy()) {
    report_fatal_error("Only 16, 32, and 64 bit floating points are supported "
                       "for ARM64EC thunks");
  }
 
  auto &DL = M->getDataLayout();
 
  if (auto *StructTy = dyn_cast<StructType>(T))
    if (StructTy->getNumElements() == 1)
      T = StructTy->getElementType(0);
 
  if (T->isArrayTy()) {
    Type *ElementTy = T->getArrayElementType();
    uint64_t ElementCnt = T->getArrayNumElements();
    uint64_t ElementSizePerBytes = DL.getTypeSizeInBits(ElementTy) / 8;
    uint64_t TotalSizeBytes = ElementCnt * ElementSizePerBytes;
    if (ElementTy->isHalfTy() || ElementTy->isFloatTy() ||
        ElementTy->isDoubleTy()) {
      if (ElementTy->isHalfTy())
        // Prefix with `llvm` since MSVC doesn't specify `_Float16`
        Out << "__llvm_H__";
      else if (ElementTy->isFloatTy())
        Out << "F";
      else if (ElementTy->isDoubleTy())
        Out << "D";
      Out << TotalSizeBytes;
      if (Alignment.value() >= 16 && !Ret)
        Out << "a" << Alignment.value();
      if (TotalSizeBytes <= 8) {
        // Arm64 returns small structs of float/double in float registers;
        // X64 uses RAX.
        return bitcast(T, TotalSizeBytes);
      } else {
        // Struct is passed directly on Arm64, but indirectly on X64.
        return pointerIndirection(T);
      }
    } else if (T->isFloatingPointTy()) {
      report_fatal_error(
          "Only 16, 32, and 64 bit floating points are supported "
          "for ARM64EC thunks");
    }
  }
 
  if ((T->isIntegerTy() || T->isPointerTy()) && DL.getTypeSizeInBits(T) <= 64) {
    Out << "i8";
    return direct(I64Ty);
  }
 
  unsigned TypeSize = ArgSizeBytes;
  if (TypeSize == 0)
    TypeSize = DL.getTypeSizeInBits(T) / 8;
  Out << "m";
  if (TypeSize != 4)
    Out << TypeSize;
  if (Alignment.value() >= 16 && !Ret)
    Out << "a" << Alignment.value();
  // FIXME: Try to canonicalize Arm64Ty more thoroughly?
  if (TypeSize == 1 || TypeSize == 2 || TypeSize == 4 || TypeSize == 8) {
    // Pass directly in an integer register
    return bitcast(T, TypeSize);
  } else {
    // Passed directly on Arm64, but indirectly on X64.
    return pointerIndirection(T);
  }
}
 
// This function builds the "exit thunk", a function which translates
// arguments and return values when calling x64 code from AArch64 code.
Function *AArch64Arm64ECCallLowering::buildExitThunk(FunctionType *FT,
                                                     AttributeList Attrs) {
  SmallString<256> ExitThunkName;
  llvm::raw_svector_ostream ExitThunkStream(ExitThunkName);
  FunctionType *Arm64Ty, *X64Ty;
  SmallVector<ThunkArgTranslation> ArgTranslations;
  getThunkType(FT, Attrs, Arm64ECThunkType::Exit, ExitThunkStream, Arm64Ty,
               X64Ty, ArgTranslations);
  if (Function *F = M->getFunction(ExitThunkName))
    return F;
 
  Function *F = Function::Create(Arm64Ty, GlobalValue::LinkOnceODRLinkage, 0,
                                 ExitThunkName, M);
  F->setCallingConv(CallingConv::ARM64EC_Thunk_Native);
  F->setSection(".wowthk$aa");
  F->setComdat(M->getOrInsertComdat(ExitThunkName));
  // Copy MSVC, and always set up a frame pointer. (Maybe this isn't necessary.)
  F->addFnAttr("frame-pointer", "all");
  // Only copy sret from the first argument. For C++ instance methods, clang can
  // stick an sret marking on a later argument, but it doesn't actually affect
  // the ABI, so we can omit it. This avoids triggering a verifier assertion.
  if (FT->getNumParams()) {
    auto SRet = Attrs.getParamAttr(0, Attribute::StructRet);
    auto InReg = Attrs.getParamAttr(0, Attribute::InReg);
    if (SRet.isValid() && !InReg.isValid())
      F->addParamAttr(1, SRet);
  }
  // FIXME: Copy anything other than sret?  Shouldn't be necessary for normal
  // C ABI, but might show up in other cases.
  BasicBlock *BB = BasicBlock::Create(M->getContext(), "", F);
  IRBuilder<> IRB(BB);
  Value *CalleePtr =
      M->getOrInsertGlobal("__os_arm64x_dispatch_call_no_redirect", PtrTy);
  Value *Callee = IRB.CreateLoad(PtrTy, CalleePtr);
  auto &DL = M->getDataLayout();
  SmallVector<Value *> Args;
 
  // Pass the called function in x9.
  auto X64TyOffset = 1;
  Args.push_back(F->arg_begin());
 
  Type *RetTy = Arm64Ty->getReturnType();
  if (RetTy != X64Ty->getReturnType()) {
    // If the return type is an array or struct, translate it. Values of size
    // 8 or less go into RAX; bigger values go into memory, and we pass a
    // pointer.
    if (DL.getTypeStoreSize(RetTy) > 8) {
      Args.push_back(IRB.CreateAlloca(RetTy));
      X64TyOffset++;
    }
  }
 
  for (auto [Arg, X64ArgType, ArgTranslation] : llvm::zip_equal(
           make_range(F->arg_begin() + 1, F->arg_end()),
           make_range(X64Ty->param_begin() + X64TyOffset, X64Ty->param_end()),
           ArgTranslations)) {
    // Translate arguments from AArch64 calling convention to x86 calling
    // convention.
    //
    // For simple types, we don't need to do any translation: they're
    // represented the same way. (Implicit sign extension is not part of
    // either convention.)
    //
    // The big thing we have to worry about is struct types... but
    // fortunately AArch64 clang is pretty friendly here: the cases that need
    // translation are always passed as a struct or array. (If we run into
    // some cases where this doesn't work, we can teach clang to mark it up
    // with an attribute.)
    //
    // The first argument is the called function, stored in x9.
    if (ArgTranslation != ThunkArgTranslation::Direct) {
      Value *Mem = IRB.CreateAlloca(Arg.getType());
      IRB.CreateStore(&Arg, Mem);
      if (ArgTranslation == ThunkArgTranslation::Bitcast) {
        Type *IntTy = IRB.getIntNTy(DL.getTypeStoreSizeInBits(Arg.getType()));
        Args.push_back(IRB.CreateLoad(IntTy, Mem));
      } else {
        assert(ArgTranslation == ThunkArgTranslation::PointerIndirection);
        Args.push_back(Mem);
      }
    } else {
      Args.push_back(&Arg);
    }
    assert(Args.back()->getType() == X64ArgType);
  }
  // FIXME: Transfer necessary attributes? sret? anything else?
 
  CallInst *Call = IRB.CreateCall(X64Ty, Callee, Args);
  Call->setCallingConv(CallingConv::ARM64EC_Thunk_X64);
 
  Value *RetVal = Call;
  if (RetTy != X64Ty->getReturnType()) {
    // If we rewrote the return type earlier, convert the return value to
    // the proper type.
    if (DL.getTypeStoreSize(RetTy) > 8) {
      RetVal = IRB.CreateLoad(RetTy, Args[1]);
    } else {
      Value *CastAlloca = IRB.CreateAlloca(RetTy);
      IRB.CreateStore(Call, CastAlloca);
      RetVal = IRB.CreateLoad(RetTy, CastAlloca);
    }
  }
 
  if (RetTy->isVoidTy())
    IRB.CreateRetVoid();
  else
    IRB.CreateRet(RetVal);
  return F;
}
 
// This function builds the "entry thunk", a function which translates
// arguments and return values when calling AArch64 code from x64 code.
Function *AArch64Arm64ECCallLowering::buildEntryThunk(Function *F) {
  SmallString<256> EntryThunkName;
  llvm::raw_svector_ostream EntryThunkStream(EntryThunkName);
  FunctionType *Arm64Ty, *X64Ty;
  SmallVector<ThunkArgTranslation> ArgTranslations;
  getThunkType(F->getFunctionType(), F->getAttributes(),
               Arm64ECThunkType::Entry, EntryThunkStream, Arm64Ty, X64Ty,
               ArgTranslations);
  if (Function *F = M->getFunction(EntryThunkName))
    return F;
 
  Function *Thunk = Function::Create(X64Ty, GlobalValue::LinkOnceODRLinkage, 0,
                                     EntryThunkName, M);
  Thunk->setCallingConv(CallingConv::ARM64EC_Thunk_X64);
  Thunk->setSection(".wowthk$aa");
  Thunk->setComdat(M->getOrInsertComdat(EntryThunkName));
  // Copy MSVC, and always set up a frame pointer. (Maybe this isn't necessary.)
  Thunk->addFnAttr("frame-pointer", "all");
 
  BasicBlock *BB = BasicBlock::Create(M->getContext(), "", Thunk);
  IRBuilder<> IRB(BB);
 
  Type *RetTy = Arm64Ty->getReturnType();
  Type *X64RetType = X64Ty->getReturnType();
 
  bool TransformDirectToSRet = X64RetType->isVoidTy() && !RetTy->isVoidTy();
  unsigned ThunkArgOffset = TransformDirectToSRet ? 2 : 1;
  unsigned PassthroughArgSize =
      (F->isVarArg() ? 5 : Thunk->arg_size()) - ThunkArgOffset;
  assert(ArgTranslations.size() == (F->isVarArg() ? 5 : PassthroughArgSize));
 
  // Translate arguments to call.
  SmallVector<Value *> Args;
  for (unsigned i = 0; i != PassthroughArgSize; ++i) {
    Value *Arg = Thunk->getArg(i + ThunkArgOffset);
    Type *ArgTy = Arm64Ty->getParamType(i);
    ThunkArgTranslation ArgTranslation = ArgTranslations[i];
    if (ArgTranslation != ThunkArgTranslation::Direct) {
      // Translate array/struct arguments to the expected type.
      if (ArgTranslation == ThunkArgTranslation::Bitcast) {
        Value *CastAlloca = IRB.CreateAlloca(ArgTy);
        IRB.CreateStore(Arg, CastAlloca);
        Arg = IRB.CreateLoad(ArgTy, CastAlloca);
      } else {
        assert(ArgTranslation == ThunkArgTranslation::PointerIndirection);
        Arg = IRB.CreateLoad(ArgTy, Arg);
      }
    }
    assert(Arg->getType() == ArgTy);
    Args.push_back(Arg);
  }
 
  if (F->isVarArg()) {
    // The 5th argument to variadic entry thunks is used to model the x64 sp
    // which is passed to the thunk in x4, this can be passed to the callee as
    // the variadic argument start address after skipping over the 32 byte
    // shadow store.
 
    // The EC thunk CC will assign any argument marked as InReg to x4.
    Thunk->addParamAttr(5, Attribute::InReg);
    Value *Arg = Thunk->getArg(5);
    Arg = IRB.CreatePtrAdd(Arg, IRB.getInt64(0x20));
    Args.push_back(Arg);
 
    // Pass in a zero variadic argument size (in x5).
    Args.push_back(IRB.getInt64(0));
  }
 
  // Call the function passed to the thunk.
  Value *Callee = Thunk->getArg(0);
  CallInst *Call = IRB.CreateCall(Arm64Ty, Callee, Args);
 
  auto SRetAttr = F->getAttributes().getParamAttr(0, Attribute::StructRet);
  auto InRegAttr = F->getAttributes().getParamAttr(0, Attribute::InReg);
  if (SRetAttr.isValid() && !InRegAttr.isValid()) {
    Thunk->addParamAttr(1, SRetAttr);
    Call->addParamAttr(0, SRetAttr);
  }
 
  Value *RetVal = Call;
  if (TransformDirectToSRet) {
    // The x64 side returns this value indirectly via a hidden pointer (sret).
    // Mark the thunk's pointer arg with sret so that ISel saves it and copies
    // it into x8 (RAX) on return, matching the x64 calling convention.
    Thunk->addParamAttr(
        1, Attribute::getWithStructRetType(M->getContext(), RetTy));
    IRB.CreateStore(RetVal, Thunk->getArg(1));
  } else if (X64RetType != RetTy) {
    Value *CastAlloca = IRB.CreateAlloca(X64RetType);
    IRB.CreateStore(Call, CastAlloca);
    RetVal = IRB.CreateLoad(X64RetType, CastAlloca);
  }
 
  // Return to the caller.  Note that the isel has code to translate this
  // "ret" to a tail call to __os_arm64x_dispatch_ret.  (Alternatively, we
  // could emit a tail call here, but that would require a dedicated calling
  // convention, which seems more complicated overall.)
  if (X64RetType->isVoidTy())
    IRB.CreateRetVoid();
  else
    IRB.CreateRet(RetVal);
 
  return Thunk;
}
 
std::optional<std::string> getArm64ECMangledFunctionName(GlobalValue &GV) {
  if (!GV.hasName()) {
    GV.setName("__unnamed");
  }
 
  return llvm::getArm64ECMangledFunctionName(GV.getName());
}
 
// Builds the "guest exit thunk", a helper to call a function which may or may
// not be an exit thunk. (We optimistically assume non-dllimport function
// declarations refer to functions defined in AArch64 code; if the linker
// can't prove that, we use this routine instead.)
Function *AArch64Arm64ECCallLowering::buildGuestExitThunk(Function *F) {
  llvm::raw_null_ostream NullThunkName;
  FunctionType *Arm64Ty, *X64Ty;
  SmallVector<ThunkArgTranslation> ArgTranslations;
  getThunkType(F->getFunctionType(), F->getAttributes(),
               Arm64ECThunkType::GuestExit, NullThunkName, Arm64Ty, X64Ty,
               ArgTranslations);
  auto MangledName = getArm64ECMangledFunctionName(*F);
  assert(MangledName && "Can't guest exit to function that's already native");
  std::string ThunkName = *MangledName;
  if (ThunkName[0] == '?' && ThunkName.find("@") != std::string::npos) {
    ThunkName.insert(ThunkName.find("@"), "$exit_thunk");
  } else {
    ThunkName.append("$exit_thunk");
  }
  Function *GuestExit =
      Function::Create(Arm64Ty, GlobalValue::WeakODRLinkage, 0, ThunkName, M);
  GuestExit->setComdat(M->getOrInsertComdat(ThunkName));
  GuestExit->setSection(".wowthk$aa");
  GuestExit->addMetadata(
      "arm64ec_unmangled_name",
      *MDNode::get(M->getContext(),
                   MDString::get(M->getContext(), F->getName())));
  GuestExit->setMetadata(
      "arm64ec_ecmangled_name",
      MDNode::get(M->getContext(),
                  MDString::get(M->getContext(), *MangledName)));
  F->setMetadata("arm64ec_hasguestexit", MDNode::get(M->getContext(), {}));
  BasicBlock *BB = BasicBlock::Create(M->getContext(), "", GuestExit);
  IRBuilder<> B(BB);
 
  // Create new call instruction. The call check should always be a call,
  // even if the original CallBase is an Invoke or CallBr instructio.
  // This is treated as a direct call, so do not use GuardFnCFGlobal.
  LoadInst *GuardCheckLoad = B.CreateLoad(PtrTy, GuardFnGlobal);
  Function *Thunk = buildExitThunk(F->getFunctionType(), F->getAttributes());
  CallInst *GuardCheck = B.CreateCall(
      GuardFnType, GuardCheckLoad, {F, Thunk});
  Value *GuardCheckDest = B.CreateExtractValue(GuardCheck, 0);
  Value *GuardFinalDest = B.CreateExtractValue(GuardCheck, 1);
 
  // Ensure that the first argument is passed in the correct register.
  GuardCheck->setCallingConv(CallingConv::CFGuard_Check);
 
  SmallVector<Value *> Args(llvm::make_pointer_range(GuestExit->args()));
  OperandBundleDef OB("cfguardtarget", GuardFinalDest);
  CallInst *Call = B.CreateCall(Arm64Ty, GuardCheckDest, Args, OB);
  Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
 
  if (Call->getType()->isVoidTy())
    B.CreateRetVoid();
  else
    B.CreateRet(Call);
 
  auto SRetAttr = F->getAttributes().getParamAttr(0, Attribute::StructRet);
  auto InRegAttr = F->getAttributes().getParamAttr(0, Attribute::InReg);
  if (SRetAttr.isValid() && !InRegAttr.isValid()) {
    GuestExit->addParamAttr(0, SRetAttr);
    Call->addParamAttr(0, SRetAttr);
  }
 
  return GuestExit;
}
 
Function *
AArch64Arm64ECCallLowering::buildPatchableThunk(GlobalAlias *UnmangledAlias,
                                                GlobalAlias *MangledAlias) {
  llvm::raw_null_ostream NullThunkName;
  FunctionType *Arm64Ty, *X64Ty;
  Function *F = cast<Function>(MangledAlias->getAliasee());
  SmallVector<ThunkArgTranslation> ArgTranslations;
  getThunkType(F->getFunctionType(), F->getAttributes(),
               Arm64ECThunkType::GuestExit, NullThunkName, Arm64Ty, X64Ty,
               ArgTranslations);
  std::string ThunkName(MangledAlias->getName());
  if (ThunkName[0] == '?' && ThunkName.find("@") != std::string::npos) {
    ThunkName.insert(ThunkName.find("@"), "$hybpatch_thunk");
  } else {
    ThunkName.append("$hybpatch_thunk");
  }
 
  Function *GuestExit =
      Function::Create(Arm64Ty, GlobalValue::WeakODRLinkage, 0, ThunkName, M);
  GuestExit->setComdat(M->getOrInsertComdat(ThunkName));
  GuestExit->setSection(".wowthk$aa");
  BasicBlock *BB = BasicBlock::Create(M->getContext(), "", GuestExit);
  IRBuilder<> B(BB);
 
  // Load the global symbol as a pointer to the check function.
  LoadInst *DispatchLoad = B.CreateLoad(PtrTy, DispatchFnGlobal);
 
  // Create new dispatch call instruction.
  Function *ExitThunk =
      buildExitThunk(F->getFunctionType(), F->getAttributes());
  CallInst *Dispatch =
      B.CreateCall(DispatchFnType, DispatchLoad,
                   {UnmangledAlias, ExitThunk, UnmangledAlias->getAliasee()});
 
  // Ensure that the first arguments are passed in the correct registers.
  Dispatch->setCallingConv(CallingConv::CFGuard_Check);
 
  SmallVector<Value *> Args(llvm::make_pointer_range(GuestExit->args()));
  CallInst *Call = B.CreateCall(Arm64Ty, Dispatch, Args);
  Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
 
  if (Call->getType()->isVoidTy())
    B.CreateRetVoid();
  else
    B.CreateRet(Call);
 
  auto SRetAttr = F->getAttributes().getParamAttr(0, Attribute::StructRet);
  auto InRegAttr = F->getAttributes().getParamAttr(0, Attribute::InReg);
  if (SRetAttr.isValid() && !InRegAttr.isValid()) {
    GuestExit->addParamAttr(0, SRetAttr);
    Call->addParamAttr(0, SRetAttr);
  }
 
  MangledAlias->setAliasee(GuestExit);
  return GuestExit;
}
 
// Lower an indirect call with inline code.
void AArch64Arm64ECCallLowering::lowerCall(CallBase *CB) {
  IRBuilder<> B(CB);
  Value *CalledOperand = CB->getCalledOperand();
 
  // If the indirect call is called within catchpad or cleanuppad,
  // we need to copy "funclet" bundle of the call.
  SmallVector<llvm::OperandBundleDef, 1> Bundles;
  if (auto Bundle = CB->getOperandBundle(LLVMContext::OB_funclet))
    Bundles.push_back(OperandBundleDef(*Bundle));
 
  // Load the global symbol as a pointer to the check function.
  Value *GuardFn;
  if ((CFGuardModuleFlag == ControlFlowGuardMode::Enabled) &&
      !CB->hasFnAttr("guard_nocf"))
    GuardFn = GuardFnCFGlobal;
  else
    GuardFn = GuardFnGlobal;
  LoadInst *GuardCheckLoad = B.CreateLoad(PtrTy, GuardFn);
 
  // Create new call instruction. The CFGuard check should always be a call,
  // even if the original CallBase is an Invoke or CallBr instruction.
  Function *Thunk = buildExitThunk(CB->getFunctionType(), CB->getAttributes());
  CallInst *GuardCheck =
      B.CreateCall(GuardFnType, GuardCheckLoad, {CalledOperand, Thunk},
                   Bundles);
  Value *GuardCheckDest = B.CreateExtractValue(GuardCheck, 0);
  Value *GuardFinalDest = B.CreateExtractValue(GuardCheck, 1);
 
  // Ensure that the first argument is passed in the correct register.
  GuardCheck->setCallingConv(CallingConv::CFGuard_Check);
 
  // Update the call: set the callee, and add a bundle with the final
  // destination,
  CB->setCalledOperand(GuardCheckDest);
  OperandBundleDef OB("cfguardtarget", GuardFinalDest);
  auto *NewCall = CallBase::addOperandBundle(CB, LLVMContext::OB_cfguardtarget,
                                             OB, CB->getIterator());
  NewCall->copyMetadata(*CB);
  CB->replaceAllUsesWith(NewCall);
  CB->eraseFromParent();
}
 
bool AArch64Arm64ECCallLowering::runOnModule(Module &Mod) {
  if (!GenerateThunks)
    return false;
 
  M = &Mod;
 
  // Check if this module has the cfguard flag and read its value.
  CFGuardModuleFlag = M->getControlFlowGuardMode();
 
  // Warn if the module flag requests an unsupported CFGuard mechanism.
  if (CFGuardModuleFlag == ControlFlowGuardMode::Enabled) {
    if (auto *CI = mdconst::dyn_extract_or_null<ConstantInt>(
            Mod.getModuleFlag("cfguard-mechanism"))) {
      auto MechanismOverride =
          static_cast<ControlFlowGuardMechanism>(CI->getZExtValue());
      if (MechanismOverride != ControlFlowGuardMechanism::Automatic &&
          MechanismOverride != ControlFlowGuardMechanism::Check)
        Mod.getContext().diagnose(
            DiagnosticInfoGeneric("only the Check Control Flow Guard mechanism "
                                  "is supported for Arm64EC",
                                  DS_Warning));
    }
  }
 
  PtrTy = PointerType::getUnqual(M->getContext());
  I64Ty = Type::getInt64Ty(M->getContext());
  VoidTy = Type::getVoidTy(M->getContext());
 
  GuardFnType =
      FunctionType::get(StructType::get(PtrTy, PtrTy), {PtrTy, PtrTy}, false);
  DispatchFnType = FunctionType::get(PtrTy, {PtrTy, PtrTy, PtrTy}, false);
  GuardFnCFGlobal = M->getOrInsertGlobal("__os_arm64x_check_icall_cfg", PtrTy);
  GuardFnGlobal = M->getOrInsertGlobal("__os_arm64x_check_icall", PtrTy);
  DispatchFnGlobal = M->getOrInsertGlobal("__os_arm64x_dispatch_call", PtrTy);
 
  // Mangle names of function aliases and add the alias name to
  // arm64ec_unmangled_name metadata to ensure a weak anti-dependency symbol is
  // emitted for the alias as well. Do this early, before handling
  // hybrid_patchable functions, to avoid mangling their aliases.
  for (GlobalAlias &A : Mod.aliases()) {
    auto F = dyn_cast_or_null<Function>(A.getAliaseeObject());
    if (!F)
      continue;
    if (std::optional<std::string> MangledName =
            getArm64ECMangledFunctionName(A)) {
      F->addMetadata("arm64ec_unmangled_name",
                     *MDNode::get(M->getContext(),
                                  MDString::get(M->getContext(), A.getName())));
      A.setName(MangledName.value());
    }
  }
 
  DenseMap<GlobalAlias *, GlobalAlias *> FnsMap;
  SetVector<GlobalAlias *> PatchableFns;
 
  for (Function &F : Mod) {
    if (F.hasPersonalityFn()) {
      GlobalValue *PersFn =
          cast<GlobalValue>(F.getPersonalityFn()->stripPointerCasts());
      if (PersFn->getValueType() && PersFn->getValueType()->isFunctionTy()) {
        if (std::optional<std::string> MangledName =
                getArm64ECMangledFunctionName(*PersFn)) {
          PersFn->setName(MangledName.value());
        }
      }
    }
 
    if (!F.hasFnAttribute(Attribute::HybridPatchable) ||
        F.isDeclarationForLinker() || F.hasLocalLinkage() ||
        F.getName().ends_with(HybridPatchableTargetSuffix))
      continue;
 
    // Rename hybrid patchable functions and change callers to use a global
    // alias instead.
    if (std::optional<std::string> MangledName =
            getArm64ECMangledFunctionName(F)) {
      std::string OrigName(F.getName());
      F.setName(MangledName.value() + HybridPatchableTargetSuffix);
 
      // The unmangled symbol is a weak alias to an undefined symbol with the
      // "EXP+" prefix. This undefined symbol is resolved by the linker by
      // creating an x86 thunk that jumps back to the actual EC target. Since we
      // can't represent that in IR, we create an alias to the target instead.
      // The "EXP+" symbol is set as metadata, which is then used by
      // emitGlobalAlias to emit the right alias.
      auto *A =
          GlobalAlias::create(GlobalValue::LinkOnceODRLinkage, OrigName, &F);
      auto *AM = GlobalAlias::create(GlobalValue::LinkOnceODRLinkage,
                                     MangledName.value(), &F);
      F.replaceUsesWithIf(AM,
                          [](Use &U) { return isa<GlobalAlias>(U.getUser()); });
      F.replaceAllUsesWith(A);
      F.setMetadata("arm64ec_exp_name",
                    MDNode::get(M->getContext(),
                                MDString::get(M->getContext(),
                                              "EXP+" + MangledName.value())));
      A->setAliasee(&F);
      AM->setAliasee(&F);
 
      if (F.hasDLLExportStorageClass()) {
        A->setDLLStorageClass(GlobalValue::DLLExportStorageClass);
        F.setDLLStorageClass(GlobalValue::DefaultStorageClass);
      }
 
      FnsMap[A] = AM;
      PatchableFns.insert(A);
    }
  }
 
  SetVector<GlobalValue *> DirectCalledFns;
  for (Function &F : Mod)
    if (!F.isDeclarationForLinker() &&
        F.getCallingConv() != CallingConv::ARM64EC_Thunk_Native &&
        F.getCallingConv() != CallingConv::ARM64EC_Thunk_X64)
      processFunction(F, DirectCalledFns, FnsMap);
 
  struct ThunkInfo {
    Constant *Src;
    Constant *Dst;
    Arm64ECThunkType Kind;
  };
  SmallVector<ThunkInfo> ThunkMapping;
  for (Function &F : Mod) {
    if (!F.isDeclarationForLinker() &&
        (!F.hasLocalLinkage() || F.hasAddressTaken()) &&
        F.getCallingConv() != CallingConv::ARM64EC_Thunk_Native &&
        F.getCallingConv() != CallingConv::ARM64EC_Thunk_X64) {
      if (!F.hasComdat())
        F.setComdat(Mod.getOrInsertComdat(F.getName()));
      ThunkMapping.push_back(
          {&F, buildEntryThunk(&F), Arm64ECThunkType::Entry});
    }
  }
  for (GlobalValue *O : DirectCalledFns) {
    auto GA = dyn_cast<GlobalAlias>(O);
    auto F = dyn_cast<Function>(GA ? GA->getAliasee() : O);
    ThunkMapping.push_back(
        {O, buildExitThunk(F->getFunctionType(), F->getAttributes()),
         Arm64ECThunkType::Exit});
    if (!GA && !F->hasDLLImportStorageClass())
      ThunkMapping.push_back(
          {buildGuestExitThunk(F), F, Arm64ECThunkType::GuestExit});
  }
  for (GlobalAlias *A : PatchableFns) {
    Function *Thunk = buildPatchableThunk(A, FnsMap[A]);
    ThunkMapping.push_back({Thunk, A, Arm64ECThunkType::GuestExit});
  }
 
  if (!ThunkMapping.empty()) {
    SmallVector<Constant *> ThunkMappingArrayElems;
    for (ThunkInfo &Thunk : ThunkMapping) {
      ThunkMappingArrayElems.push_back(ConstantStruct::getAnon(
          {Thunk.Src, Thunk.Dst,
           ConstantInt::get(M->getContext(), APInt(32, uint8_t(Thunk.Kind)))}));
    }
    Constant *ThunkMappingArray = ConstantArray::get(
        llvm::ArrayType::get(ThunkMappingArrayElems[0]->getType(),
                             ThunkMappingArrayElems.size()),
        ThunkMappingArrayElems);
    new GlobalVariable(Mod, ThunkMappingArray->getType(), /*isConstant*/ false,
                       GlobalValue::ExternalLinkage, ThunkMappingArray,
                       "llvm.arm64ec.symbolmap");
  }
 
  return true;
}
 
bool AArch64Arm64ECCallLowering::processFunction(
    Function &F, SetVector<GlobalValue *> &DirectCalledFns,
    DenseMap<GlobalAlias *, GlobalAlias *> &FnsMap) {
  SmallVector<CallBase *, 8> IndirectCalls;
 
  // For ARM64EC targets, a function definition's name is mangled differently
  // from the normal symbol. We currently have no representation of this sort
  // of symbol in IR, so we change the name to the mangled name, then store
  // the unmangled name as metadata.  Later passes that need the unmangled
  // name (emitting the definition) can grab it from the metadata.
  //
  // FIXME: Handle functions with weak linkage?
  if (!F.hasLocalLinkage() || F.hasAddressTaken()) {
    if (std::optional<std::string> MangledName =
            getArm64ECMangledFunctionName(F)) {
      F.addMetadata("arm64ec_unmangled_name",
                    *MDNode::get(M->getContext(),
                                 MDString::get(M->getContext(), F.getName())));
      if (F.hasComdat() && F.getComdat()->getName() == F.getName()) {
        Comdat *MangledComdat = M->getOrInsertComdat(MangledName.value());
        SmallVector<GlobalObject *> ComdatUsers =
            to_vector(F.getComdat()->getUsers());
        for (GlobalObject *User : ComdatUsers)
          User->setComdat(MangledComdat);
      }
      F.setName(MangledName.value());
    }
  }
 
  // Iterate over the instructions to find all indirect call/invoke/callbr
  // instructions. Make a separate list of pointers to indirect
  // call/invoke/callbr instructions because the original instructions will be
  // deleted as the checks are added.
  for (BasicBlock &BB : F) {
    for (Instruction &I : BB) {
      auto *CB = dyn_cast<CallBase>(&I);
      if (!CB || CB->getCallingConv() == CallingConv::ARM64EC_Thunk_X64 ||
          CB->isInlineAsm())
        continue;
 
      // We need to instrument any call that isn't directly calling an
      // ARM64 function.
      //
      // FIXME: getCalledFunction() fails if there's a bitcast (e.g.
      // unprototyped functions in C)
      if (Function *F = CB->getCalledFunction()) {
        if (!LowerDirectToIndirect || F->hasLocalLinkage() ||
            F->isIntrinsic() || !F->isDeclarationForLinker())
          continue;
 
        DirectCalledFns.insert(F);
        continue;
      }
 
      // Use mangled global alias for direct calls to patchable functions.
      if (GlobalAlias *A = dyn_cast<GlobalAlias>(CB->getCalledOperand())) {
        auto I = FnsMap.find(A);
        if (I != FnsMap.end()) {
          CB->setCalledOperand(I->second);
          DirectCalledFns.insert(I->first);
          continue;
        }
      }
 
      IndirectCalls.push_back(CB);
      ++Arm64ECCallsLowered;
    }
  }
 
  if (IndirectCalls.empty())
    return false;
 
  for (CallBase *CB : IndirectCalls)
    lowerCall(CB);
 
  return true;
}
 
char AArch64Arm64ECCallLowering::ID = 0;
INITIALIZE_PASS(AArch64Arm64ECCallLowering, "Arm64ECCallLowering",
                "AArch64Arm64ECCallLowering", false, false)
 
ModulePass *llvm::createAArch64Arm64ECCallLoweringPass() {
  return new AArch64Arm64ECCallLowering;
}