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cb8447ad52
becomes reachable when before it wasn't). Check to make sure that it's not null before trying to use it. llvm-svn: 128434
264 lines
9.0 KiB
C++
264 lines
9.0 KiB
C++
//===-- StackProtector.cpp - Stack Protector Insertion --------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass inserts stack protectors into functions which need them. A variable
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// with a random value in it is stored onto the stack before the local variables
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// are allocated. Upon exiting the block, the stored value is checked. If it's
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// changed, then there was some sort of violation and the program aborts.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "stack-protector"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Attributes.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Target/TargetLowering.h"
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using namespace llvm;
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// SSPBufferSize - The lower bound for a buffer to be considered for stack
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// smashing protection.
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static cl::opt<unsigned>
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SSPBufferSize("stack-protector-buffer-size", cl::init(8),
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cl::desc("Lower bound for a buffer to be considered for "
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"stack protection"));
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namespace {
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class StackProtector : public FunctionPass {
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/// TLI - Keep a pointer of a TargetLowering to consult for determining
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/// target type sizes.
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const TargetLowering *TLI;
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Function *F;
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Module *M;
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DominatorTree* DT;
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/// InsertStackProtectors - Insert code into the prologue and epilogue of
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/// the function.
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///
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/// - The prologue code loads and stores the stack guard onto the stack.
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/// - The epilogue checks the value stored in the prologue against the
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/// original value. It calls __stack_chk_fail if they differ.
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bool InsertStackProtectors();
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/// CreateFailBB - Create a basic block to jump to when the stack protector
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/// check fails.
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BasicBlock *CreateFailBB();
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/// RequiresStackProtector - Check whether or not this function needs a
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/// stack protector based upon the stack protector level.
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bool RequiresStackProtector() const;
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public:
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static char ID; // Pass identification, replacement for typeid.
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StackProtector() : FunctionPass(ID), TLI(0) {
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initializeStackProtectorPass(*PassRegistry::getPassRegistry());
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}
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StackProtector(const TargetLowering *tli)
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: FunctionPass(ID), TLI(tli) {
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initializeStackProtectorPass(*PassRegistry::getPassRegistry());
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addPreserved<DominatorTree>();
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}
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virtual bool runOnFunction(Function &Fn);
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};
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} // end anonymous namespace
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char StackProtector::ID = 0;
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INITIALIZE_PASS(StackProtector, "stack-protector",
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"Insert stack protectors", false, false)
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FunctionPass *llvm::createStackProtectorPass(const TargetLowering *tli) {
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return new StackProtector(tli);
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}
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bool StackProtector::runOnFunction(Function &Fn) {
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F = &Fn;
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M = F->getParent();
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DT = getAnalysisIfAvailable<DominatorTree>();
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if (!RequiresStackProtector()) return false;
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return InsertStackProtectors();
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}
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/// RequiresStackProtector - Check whether or not this function needs a stack
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/// protector based upon the stack protector level. The heuristic we use is to
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/// add a guard variable to functions that call alloca, and functions with
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/// buffers larger than SSPBufferSize bytes.
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bool StackProtector::RequiresStackProtector() const {
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if (F->hasFnAttr(Attribute::StackProtectReq))
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return true;
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if (!F->hasFnAttr(Attribute::StackProtect))
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return false;
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const TargetData *TD = TLI->getTargetData();
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for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
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BasicBlock *BB = I;
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for (BasicBlock::iterator
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II = BB->begin(), IE = BB->end(); II != IE; ++II)
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if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
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if (AI->isArrayAllocation())
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// This is a call to alloca with a variable size. Emit stack
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// protectors.
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return true;
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if (const ArrayType *AT = dyn_cast<ArrayType>(AI->getAllocatedType())) {
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// We apparently only care about character arrays.
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if (!AT->getElementType()->isIntegerTy(8))
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continue;
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// If an array has more than SSPBufferSize bytes of allocated space,
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// then we emit stack protectors.
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if (SSPBufferSize <= TD->getTypeAllocSize(AT))
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return true;
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}
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}
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}
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return false;
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}
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/// InsertStackProtectors - Insert code into the prologue and epilogue of the
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/// function.
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///
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/// - The prologue code loads and stores the stack guard onto the stack.
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/// - The epilogue checks the value stored in the prologue against the original
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/// value. It calls __stack_chk_fail if they differ.
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bool StackProtector::InsertStackProtectors() {
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BasicBlock *FailBB = 0; // The basic block to jump to if check fails.
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BasicBlock *FailBBDom = 0; // FailBB's dominator.
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AllocaInst *AI = 0; // Place on stack that stores the stack guard.
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Value *StackGuardVar = 0; // The stack guard variable.
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for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
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BasicBlock *BB = I++;
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ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
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if (!RI) continue;
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if (!FailBB) {
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// Insert code into the entry block that stores the __stack_chk_guard
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// variable onto the stack:
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//
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// entry:
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// StackGuardSlot = alloca i8*
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// StackGuard = load __stack_chk_guard
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// call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
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//
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const PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
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unsigned AddressSpace, Offset;
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if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
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Constant *OffsetVal =
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ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);
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StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
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PointerType::get(PtrTy, AddressSpace));
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} else {
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StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
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}
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BasicBlock &Entry = F->getEntryBlock();
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Instruction *InsPt = &Entry.front();
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AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
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LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
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Value *Args[] = { LI, AI };
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CallInst::
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Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
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&Args[0], array_endof(Args), "", InsPt);
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// Create the basic block to jump to when the guard check fails.
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FailBB = CreateFailBB();
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if (DT)
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FailBBDom = DT->isReachableFromEntry(BB) ? BB : 0;
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}
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// For each block with a return instruction, convert this:
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//
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// return:
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// ...
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// ret ...
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//
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// into this:
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//
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// return:
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// ...
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// %1 = load __stack_chk_guard
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// %2 = load StackGuardSlot
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// %3 = cmp i1 %1, %2
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// br i1 %3, label %SP_return, label %CallStackCheckFailBlk
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//
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// SP_return:
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// ret ...
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//
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// CallStackCheckFailBlk:
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// call void @__stack_chk_fail()
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// unreachable
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// Split the basic block before the return instruction.
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BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
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if (DT && DT->isReachableFromEntry(BB)) {
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DT->addNewBlock(NewBB, BB);
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if (FailBBDom)
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FailBBDom = DT->findNearestCommonDominator(FailBBDom, BB);
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}
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// Remove default branch instruction to the new BB.
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BB->getTerminator()->eraseFromParent();
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// Move the newly created basic block to the point right after the old basic
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// block so that it's in the "fall through" position.
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NewBB->moveAfter(BB);
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// Generate the stack protector instructions in the old basic block.
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LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB);
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LoadInst *LI2 = new LoadInst(AI, "", true, BB);
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ICmpInst *Cmp = new ICmpInst(*BB, CmpInst::ICMP_EQ, LI1, LI2, "");
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BranchInst::Create(NewBB, FailBB, Cmp, BB);
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}
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// Return if we didn't modify any basic blocks. I.e., there are no return
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// statements in the function.
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if (!FailBB) return false;
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if (DT && FailBBDom)
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DT->addNewBlock(FailBB, FailBBDom);
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return true;
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}
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/// CreateFailBB - Create a basic block to jump to when the stack protector
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/// check fails.
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BasicBlock *StackProtector::CreateFailBB() {
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BasicBlock *FailBB = BasicBlock::Create(F->getContext(),
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"CallStackCheckFailBlk", F);
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Constant *StackChkFail =
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M->getOrInsertFunction("__stack_chk_fail",
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Type::getVoidTy(F->getContext()), NULL);
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CallInst::Create(StackChkFail, "", FailBB);
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new UnreachableInst(F->getContext(), FailBB);
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return FailBB;
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}
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