-//===-- ShadowStackCollector.cpp - GC support for uncooperative targets ---===//
+//===-- ShadowStackGC.cpp - GC support for uncooperative targets ----------===//
//
// The LLVM Compiler Infrastructure
//
//
// This file implements lowering for the llvm.gc* intrinsics for targets that do
// not natively support them (which includes the C backend). Note that the code
-// generated is not quite as efficient as collectors which generate stack maps
+// generated is not quite as efficient as algorithms which generate stack maps
// to identify roots.
//
// This pass implements the code transformation described in this paper:
// Fergus Henderson, ISMM, 2002
//
// In runtime/GC/SemiSpace.cpp is a prototype runtime which is compatible with
-// this collector.
+// ShadowStackGC.
//
// In order to support this particular transformation, all stack roots are
// coallocated in the stack. This allows a fully target-independent stack map
using namespace llvm;
namespace {
-
- class VISIBILITY_HIDDEN ShadowStackCollector : public Collector {
+
+ class ShadowStackGC : public GCStrategy {
/// RootChain - This is the global linked-list that contains the chain of GC
/// roots.
GlobalVariable *Head;
-
+
/// StackEntryTy - Abstract type of a link in the shadow stack.
- ///
+ ///
const StructType *StackEntryTy;
-
+
/// Roots - GC roots in the current function. Each is a pair of the
/// intrinsic call and its corresponding alloca.
std::vector<std::pair<CallInst*,AllocaInst*> > Roots;
-
+
public:
- ShadowStackCollector();
-
+ ShadowStackGC();
+
bool initializeCustomLowering(Module &M);
bool performCustomLowering(Function &F);
-
+
private:
bool IsNullValue(Value *V);
Constant *GetFrameMap(Function &F);
const Type* GetConcreteStackEntryType(Function &F);
void CollectRoots(Function &F);
- static GetElementPtrInst *CreateGEP(IRBuilder<> &B, Value *BasePtr,
+ static GetElementPtrInst *CreateGEP(LLVMContext &Context,
+ IRBuilder<> &B, Value *BasePtr,
int Idx1, const char *Name);
- static GetElementPtrInst *CreateGEP(IRBuilder<> &B, Value *BasePtr,
+ static GetElementPtrInst *CreateGEP(LLVMContext &Context,
+ IRBuilder<> &B, Value *BasePtr,
int Idx1, int Idx2, const char *Name);
};
}
-
-static CollectorRegistry::Add<ShadowStackCollector>
-Y("shadow-stack",
- "Very portable collector for uncooperative code generators");
-
+
+static GCRegistry::Add<ShadowStackGC>
+X("shadow-stack", "Very portable GC for uncooperative code generators");
+
namespace {
/// EscapeEnumerator - This is a little algorithm to find all escape points
/// from a function so that "finally"-style code can be inserted. In addition
/// to finding the existing return and unwind instructions, it also (if
/// necessary) transforms any call instructions into invokes and sends them to
/// a landing pad.
- ///
+ ///
/// It's wrapped up in a state machine using the same transform C# uses for
/// 'yield return' enumerators, This transform allows it to be non-allocating.
- class VISIBILITY_HIDDEN EscapeEnumerator {
+ class EscapeEnumerator {
Function &F;
const char *CleanupBBName;
-
+
// State.
int State;
Function::iterator StateBB, StateE;
IRBuilder<> Builder;
-
+
public:
EscapeEnumerator(Function &F, const char *N = "cleanup")
- : F(F), CleanupBBName(N), State(0) {}
-
+ : F(F), CleanupBBName(N), State(0), Builder(F.getContext()) {}
+
IRBuilder<> *Next() {
switch (State) {
default:
return 0;
-
+
case 0:
StateBB = F.begin();
StateE = F.end();
State = 1;
-
+
case 1:
// Find all 'return' and 'unwind' instructions.
while (StateBB != StateE) {
BasicBlock *CurBB = StateBB++;
-
+
// Branches and invokes do not escape, only unwind and return do.
TerminatorInst *TI = CurBB->getTerminator();
if (!isa<UnwindInst>(TI) && !isa<ReturnInst>(TI))
continue;
-
+
Builder.SetInsertPoint(TI->getParent(), TI);
return &Builder;
}
-
+
State = 2;
-
+
// Find all 'call' instructions.
SmallVector<Instruction*,16> Calls;
for (Function::iterator BB = F.begin(),
if (!CI->getCalledFunction() ||
!CI->getCalledFunction()->getIntrinsicID())
Calls.push_back(CI);
-
+
if (Calls.empty())
return 0;
-
+
// Create a cleanup block.
- BasicBlock *CleanupBB = BasicBlock::Create(CleanupBBName, &F);
- UnwindInst *UI = new UnwindInst(CleanupBB);
-
+ BasicBlock *CleanupBB = BasicBlock::Create(F.getContext(),
+ CleanupBBName, &F);
+ UnwindInst *UI = new UnwindInst(F.getContext(), CleanupBB);
+
// Transform the 'call' instructions into 'invoke's branching to the
// cleanup block. Go in reverse order to make prettier BB names.
SmallVector<Value*,16> Args;
for (unsigned I = Calls.size(); I != 0; ) {
CallInst *CI = cast<CallInst>(Calls[--I]);
-
+
// Split the basic block containing the function call.
BasicBlock *CallBB = CI->getParent();
BasicBlock *NewBB =
CallBB->splitBasicBlock(CI, CallBB->getName() + ".cont");
-
+
// Remove the unconditional branch inserted at the end of CallBB.
CallBB->getInstList().pop_back();
NewBB->getInstList().remove(CI);
-
+
// Create a new invoke instruction.
Args.clear();
Args.append(CI->op_begin() + 1, CI->op_end());
-
+
InvokeInst *II = InvokeInst::Create(CI->getOperand(0),
NewBB, CleanupBB,
Args.begin(), Args.end(),
CI->getName(), CallBB);
II->setCallingConv(CI->getCallingConv());
- II->setParamAttrs(CI->getParamAttrs());
+ II->setAttributes(CI->getAttributes());
CI->replaceAllUsesWith(II);
delete CI;
}
-
+
Builder.SetInsertPoint(UI->getParent(), UI);
return &Builder;
}
}
};
-
}
// -----------------------------------------------------------------------------
-Collector *llvm::createShadowStackCollector() {
- return new ShadowStackCollector();
-}
+void llvm::linkShadowStackGC() { }
-ShadowStackCollector::ShadowStackCollector() : Head(0), StackEntryTy(0) {
+ShadowStackGC::ShadowStackGC() : Head(0), StackEntryTy(0) {
InitRoots = true;
CustomRoots = true;
}
-Constant *ShadowStackCollector::GetFrameMap(Function &F) {
+Constant *ShadowStackGC::GetFrameMap(Function &F) {
// doInitialization creates the abstract type of this value.
-
- Type *VoidPtr = PointerType::getUnqual(Type::Int8Ty);
-
+ const Type *VoidPtr = Type::getInt8PtrTy(F.getContext());
+
// Truncate the ShadowStackDescriptor if some metadata is null.
unsigned NumMeta = 0;
SmallVector<Constant*,16> Metadata;
NumMeta = I + 1;
Metadata.push_back(ConstantExpr::getBitCast(C, VoidPtr));
}
-
+
Constant *BaseElts[] = {
- ConstantInt::get(Type::Int32Ty, Roots.size(), false),
- ConstantInt::get(Type::Int32Ty, NumMeta, false),
+ ConstantInt::get(Type::getInt32Ty(F.getContext()), Roots.size(), false),
+ ConstantInt::get(Type::getInt32Ty(F.getContext()), NumMeta, false),
};
-
+
Constant *DescriptorElts[] = {
- ConstantStruct::get(BaseElts, 2),
+ ConstantStruct::get(F.getContext(), BaseElts, 2, false),
ConstantArray::get(ArrayType::get(VoidPtr, NumMeta),
Metadata.begin(), NumMeta)
};
-
- Constant *FrameMap = ConstantStruct::get(DescriptorElts, 2);
-
+
+ Constant *FrameMap = ConstantStruct::get(F.getContext(), DescriptorElts, 2,
+ false);
+
std::string TypeName("gc_map.");
TypeName += utostr(NumMeta);
F.getParent()->addTypeName(TypeName, FrameMap->getType());
-
+
// FIXME: Is this actually dangerous as WritingAnLLVMPass.html claims? Seems
// that, short of multithreaded LLVM, it should be safe; all that is
// necessary is that a simple Module::iterator loop not be invalidated.
// Appending to the GlobalVariable list is safe in that sense.
- //
+ //
// All of the output passes emit globals last. The ExecutionEngine
// explicitly supports adding globals to the module after
// initialization.
- //
+ //
// Still, if it isn't deemed acceptable, then this transformation needs
// to be a ModulePass (which means it cannot be in the 'llc' pipeline
// (which uses a FunctionPassManager (which segfaults (not asserts) if
// provided a ModulePass))).
- Constant *GV = new GlobalVariable(FrameMap->getType(), true,
+ Constant *GV = new GlobalVariable(*F.getParent(), FrameMap->getType(), true,
GlobalVariable::InternalLinkage,
- FrameMap, "__gc_" + F.getName(),
- F.getParent());
-
- Constant *GEPIndices[2] = { ConstantInt::get(Type::Int32Ty, 0),
- ConstantInt::get(Type::Int32Ty, 0) };
+ FrameMap, "__gc_" + F.getName());
+
+ Constant *GEPIndices[2] = {
+ ConstantInt::get(Type::getInt32Ty(F.getContext()), 0),
+ ConstantInt::get(Type::getInt32Ty(F.getContext()), 0)
+ };
return ConstantExpr::getGetElementPtr(GV, GEPIndices, 2);
}
-const Type* ShadowStackCollector::GetConcreteStackEntryType(Function &F) {
+const Type* ShadowStackGC::GetConcreteStackEntryType(Function &F) {
// doInitialization creates the generic version of this type.
std::vector<const Type*> EltTys;
EltTys.push_back(StackEntryTy);
for (size_t I = 0; I != Roots.size(); I++)
EltTys.push_back(Roots[I].second->getAllocatedType());
- Type *Ty = StructType::get(EltTys);
-
+ Type *Ty = StructType::get(F.getContext(), EltTys);
+
std::string TypeName("gc_stackentry.");
TypeName += F.getName();
F.getParent()->addTypeName(TypeName, Ty);
-
+
return Ty;
}
/// doInitialization - If this module uses the GC intrinsics, find them now. If
/// not, exit fast.
-bool ShadowStackCollector::initializeCustomLowering(Module &M) {
+bool ShadowStackGC::initializeCustomLowering(Module &M) {
// struct FrameMap {
// int32_t NumRoots; // Number of roots in stack frame.
// int32_t NumMeta; // Number of metadata descriptors. May be < NumRoots.
// void *Meta[]; // May be absent for roots without metadata.
// };
std::vector<const Type*> EltTys;
- EltTys.push_back(Type::Int32Ty); // 32 bits is ok up to a 32GB stack frame. :)
- EltTys.push_back(Type::Int32Ty); // Specifies length of variable length array.
- StructType *FrameMapTy = StructType::get(EltTys);
+ // 32 bits is ok up to a 32GB stack frame. :)
+ EltTys.push_back(Type::getInt32Ty(M.getContext()));
+ // Specifies length of variable length array.
+ EltTys.push_back(Type::getInt32Ty(M.getContext()));
+ StructType *FrameMapTy = StructType::get(M.getContext(), EltTys);
M.addTypeName("gc_map", FrameMapTy);
PointerType *FrameMapPtrTy = PointerType::getUnqual(FrameMapTy);
-
+
// struct StackEntry {
// ShadowStackEntry *Next; // Caller's stack entry.
// FrameMap *Map; // Pointer to constant FrameMap.
// void *Roots[]; // Stack roots (in-place array, so we pretend).
// };
- OpaqueType *RecursiveTy = OpaqueType::get();
-
+ OpaqueType *RecursiveTy = OpaqueType::get(M.getContext());
+
EltTys.clear();
EltTys.push_back(PointerType::getUnqual(RecursiveTy));
EltTys.push_back(FrameMapPtrTy);
- PATypeHolder LinkTyH = StructType::get(EltTys);
-
+ PATypeHolder LinkTyH = StructType::get(M.getContext(), EltTys);
+
RecursiveTy->refineAbstractTypeTo(LinkTyH.get());
StackEntryTy = cast<StructType>(LinkTyH.get());
const PointerType *StackEntryPtrTy = PointerType::getUnqual(StackEntryTy);
M.addTypeName("gc_stackentry", LinkTyH.get()); // FIXME: Is this safe from
// a FunctionPass?
-
+
// Get the root chain if it already exists.
Head = M.getGlobalVariable("llvm_gc_root_chain");
if (!Head) {
// If the root chain does not exist, insert a new one with linkonce
// linkage!
- Head = new GlobalVariable(StackEntryPtrTy, false,
- GlobalValue::LinkOnceLinkage,
+ Head = new GlobalVariable(M, StackEntryPtrTy, false,
+ GlobalValue::LinkOnceAnyLinkage,
Constant::getNullValue(StackEntryPtrTy),
- "llvm_gc_root_chain", &M);
+ "llvm_gc_root_chain");
} else if (Head->hasExternalLinkage() && Head->isDeclaration()) {
Head->setInitializer(Constant::getNullValue(StackEntryPtrTy));
- Head->setLinkage(GlobalValue::LinkOnceLinkage);
+ Head->setLinkage(GlobalValue::LinkOnceAnyLinkage);
}
-
+
return true;
}
-bool ShadowStackCollector::IsNullValue(Value *V) {
+bool ShadowStackGC::IsNullValue(Value *V) {
if (Constant *C = dyn_cast<Constant>(V))
return C->isNullValue();
return false;
}
-void ShadowStackCollector::CollectRoots(Function &F) {
+void ShadowStackGC::CollectRoots(Function &F) {
// FIXME: Account for original alignment. Could fragment the root array.
// Approach 1: Null initialize empty slots at runtime. Yuck.
// Approach 2: Emit a map of the array instead of just a count.
-
+
assert(Roots.empty() && "Not cleaned up?");
-
+
SmallVector<std::pair<CallInst*,AllocaInst*>,16> MetaRoots;
-
+
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;)
if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++))
else
MetaRoots.push_back(Pair);
}
-
+
// Number roots with metadata (usually empty) at the beginning, so that the
// FrameMap::Meta array can be elided.
Roots.insert(Roots.begin(), MetaRoots.begin(), MetaRoots.end());
}
GetElementPtrInst *
-ShadowStackCollector::CreateGEP(IRBuilder<> &B, Value *BasePtr,
- int Idx, int Idx2, const char *Name) {
- Value *Indices[] = { ConstantInt::get(Type::Int32Ty, 0),
- ConstantInt::get(Type::Int32Ty, Idx),
- ConstantInt::get(Type::Int32Ty, Idx2) };
+ShadowStackGC::CreateGEP(LLVMContext &Context, IRBuilder<> &B, Value *BasePtr,
+ int Idx, int Idx2, const char *Name) {
+ Value *Indices[] = { ConstantInt::get(Type::getInt32Ty(Context), 0),
+ ConstantInt::get(Type::getInt32Ty(Context), Idx),
+ ConstantInt::get(Type::getInt32Ty(Context), Idx2) };
Value* Val = B.CreateGEP(BasePtr, Indices, Indices + 3, Name);
-
+
assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant");
-
+
return dyn_cast<GetElementPtrInst>(Val);
}
GetElementPtrInst *
-ShadowStackCollector::CreateGEP(IRBuilder<> &B, Value *BasePtr,
- int Idx, const char *Name) {
- Value *Indices[] = { ConstantInt::get(Type::Int32Ty, 0),
- ConstantInt::get(Type::Int32Ty, Idx) };
+ShadowStackGC::CreateGEP(LLVMContext &Context, IRBuilder<> &B, Value *BasePtr,
+ int Idx, const char *Name) {
+ Value *Indices[] = { ConstantInt::get(Type::getInt32Ty(Context), 0),
+ ConstantInt::get(Type::getInt32Ty(Context), Idx) };
Value *Val = B.CreateGEP(BasePtr, Indices, Indices + 2, Name);
-
+
assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant");
return dyn_cast<GetElementPtrInst>(Val);
}
/// runOnFunction - Insert code to maintain the shadow stack.
-bool ShadowStackCollector::performCustomLowering(Function &F) {
+bool ShadowStackGC::performCustomLowering(Function &F) {
+ LLVMContext &Context = F.getContext();
+
// Find calls to llvm.gcroot.
CollectRoots(F);
-
+
// If there are no roots in this function, then there is no need to add a
// stack map entry for it.
if (Roots.empty())
return false;
-
+
// Build the constant map and figure the type of the shadow stack entry.
Value *FrameMap = GetFrameMap(F);
const Type *ConcreteStackEntryTy = GetConcreteStackEntryType(F);
-
+
// Build the shadow stack entry at the very start of the function.
BasicBlock::iterator IP = F.getEntryBlock().begin();
IRBuilder<> AtEntry(IP->getParent(), IP);
-
+
Instruction *StackEntry = AtEntry.CreateAlloca(ConcreteStackEntryTy, 0,
"gc_frame");
-
+
while (isa<AllocaInst>(IP)) ++IP;
AtEntry.SetInsertPoint(IP->getParent(), IP);
-
+
// Initialize the map pointer and load the current head of the shadow stack.
Instruction *CurrentHead = AtEntry.CreateLoad(Head, "gc_currhead");
- Instruction *EntryMapPtr = CreateGEP(AtEntry, StackEntry,0,1,"gc_frame.map");
+ Instruction *EntryMapPtr = CreateGEP(Context, AtEntry, StackEntry,
+ 0,1,"gc_frame.map");
AtEntry.CreateStore(FrameMap, EntryMapPtr);
-
+
// After all the allocas...
for (unsigned I = 0, E = Roots.size(); I != E; ++I) {
// For each root, find the corresponding slot in the aggregate...
- Value *SlotPtr = CreateGEP(AtEntry, StackEntry, 1 + I, "gc_root");
-
+ Value *SlotPtr = CreateGEP(Context, AtEntry, StackEntry, 1 + I, "gc_root");
+
// And use it in lieu of the alloca.
AllocaInst *OriginalAlloca = Roots[I].second;
SlotPtr->takeName(OriginalAlloca);
OriginalAlloca->replaceAllUsesWith(SlotPtr);
}
-
- // Move past the original stores inserted by Collector::InitRoots. This isn't
- // really necessary (the collector would never see the intermediate state),
- // but it's nicer not to push the half-initialized entry onto the stack.
+
+ // Move past the original stores inserted by GCStrategy::InitRoots. This isn't
+ // really necessary (the collector would never see the intermediate state at
+ // runtime), but it's nicer not to push the half-initialized entry onto the
+ // shadow stack.
while (isa<StoreInst>(IP)) ++IP;
AtEntry.SetInsertPoint(IP->getParent(), IP);
-
+
// Push the entry onto the shadow stack.
- Instruction *EntryNextPtr = CreateGEP(AtEntry,StackEntry,0,0,"gc_frame.next");
- Instruction *NewHeadVal = CreateGEP(AtEntry,StackEntry, 0, "gc_newhead");
- AtEntry.CreateStore(CurrentHead, EntryNextPtr);
- AtEntry.CreateStore(NewHeadVal, Head);
-
+ Instruction *EntryNextPtr = CreateGEP(Context, AtEntry,
+ StackEntry,0,0,"gc_frame.next");
+ Instruction *NewHeadVal = CreateGEP(Context, AtEntry,
+ StackEntry, 0, "gc_newhead");
+ AtEntry.CreateStore(CurrentHead, EntryNextPtr);
+ AtEntry.CreateStore(NewHeadVal, Head);
+
// For each instruction that escapes...
EscapeEnumerator EE(F, "gc_cleanup");
while (IRBuilder<> *AtExit = EE.Next()) {
// Pop the entry from the shadow stack. Don't reuse CurrentHead from
// AtEntry, since that would make the value live for the entire function.
- Instruction *EntryNextPtr2 = CreateGEP(*AtExit, StackEntry, 0, 0,
+ Instruction *EntryNextPtr2 = CreateGEP(Context, *AtExit, StackEntry, 0, 0,
"gc_frame.next");
Value *SavedHead = AtExit->CreateLoad(EntryNextPtr2, "gc_savedhead");
AtExit->CreateStore(SavedHead, Head);
}
-
+
// Delete the original allocas (which are no longer used) and the intrinsic
// calls (which are no longer valid). Doing this last avoids invalidating
// iterators.
Roots[I].first->eraseFromParent();
Roots[I].second->eraseFromParent();
}
-
+
Roots.clear();
return true;
}
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