#include "llvm/CodeGen/GCStrategy.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
+#include "llvm/Support/Compiler.h"
#include "llvm/Support/IRBuilder.h"
using namespace llvm;
namespace {
-
+
class VISIBILITY_HIDDEN 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:
ShadowStackGC();
-
+
bool initializeCustomLowering(Module &M);
bool performCustomLowering(Function &F);
-
+
private:
bool IsNullValue(Value *V);
Constant *GetFrameMap(Function &F);
};
}
-
+
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 {
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) {}
-
+
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);
-
+
// 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;
}
Constant *ShadowStackGC::GetFrameMap(Function &F) {
// doInitialization creates the abstract type of this value.
-
+
Type *VoidPtr = PointerType::getUnqual(Type::Int8Ty);
-
+
// 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),
};
-
+
Constant *DescriptorElts[] = {
ConstantStruct::get(BaseElts, 2),
ConstantArray::get(ArrayType::get(VoidPtr, NumMeta),
Metadata.begin(), NumMeta)
};
-
+
Constant *FrameMap = ConstantStruct::get(DescriptorElts, 2);
-
+
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
GlobalVariable::InternalLinkage,
FrameMap, "__gc_" + F.getName(),
F.getParent());
-
+
Constant *GEPIndices[2] = { ConstantInt::get(Type::Int32Ty, 0),
ConstantInt::get(Type::Int32Ty, 0) };
return ConstantExpr::getGetElementPtr(GV, GEPIndices, 2);
for (size_t I = 0; I != Roots.size(); I++)
EltTys.push_back(Roots[I].second->getAllocatedType());
Type *Ty = StructType::get(EltTys);
-
+
std::string TypeName("gc_stackentry.");
TypeName += F.getName();
F.getParent()->addTypeName(TypeName, Ty);
-
+
return Ty;
}
StructType *FrameMapTy = StructType::get(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();
-
+
EltTys.clear();
EltTys.push_back(PointerType::getUnqual(RecursiveTy));
EltTys.push_back(FrameMapPtrTy);
PATypeHolder LinkTyH = StructType::get(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) {
Head->setInitializer(Constant::getNullValue(StackEntryPtrTy));
Head->setLinkage(GlobalValue::LinkOnceLinkage);
}
-
+
return true;
}
// 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());
ConstantInt::get(Type::Int32Ty, Idx),
ConstantInt::get(Type::Int32Ty, Idx2) };
Value* Val = B.CreateGEP(BasePtr, Indices, Indices + 3, Name);
-
+
assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant");
-
+
return dyn_cast<GetElementPtrInst>(Val);
}
Value *Indices[] = { ConstantInt::get(Type::Int32Ty, 0),
ConstantInt::get(Type::Int32Ty, Idx) };
Value *Val = B.CreateGEP(BasePtr, Indices, Indices + 2, Name);
-
+
assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant");
return dyn_cast<GetElementPtrInst>(Val);
bool ShadowStackGC::performCustomLowering(Function &F) {
// 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");
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");
-
+
// 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 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);
-
+
// For each instruction that escapes...
EscapeEnumerator EE(F, "gc_cleanup");
while (IRBuilder<> *AtExit = EE.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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