From c3348a77f7e1bdc8e52a9f70fd190555df34d7c1 Mon Sep 17 00:00:00 2001 From: Bill Wendling Date: Tue, 18 Nov 2008 05:32:11 +0000 Subject: [PATCH] - Use "moveAfter" instead of "remove/insert" of a basic block. - Use less indentation in coding. - Shorten description. - Update comments. - Move code around git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59496 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/StackProtector.cpp | 207 +++++++++++++++++---------------- 1 file changed, 104 insertions(+), 103 deletions(-) diff --git a/lib/CodeGen/StackProtector.cpp b/lib/CodeGen/StackProtector.cpp index d724bd71f80..10b5d6d07f8 100644 --- a/lib/CodeGen/StackProtector.cpp +++ b/lib/CodeGen/StackProtector.cpp @@ -33,8 +33,8 @@ using namespace llvm; // smashing protection. static cl::opt SSPBufferSize("stack-protector-buffer-size", cl::init(8), - cl::desc("The lower bound for a buffer to be considered for " - "stack smashing protection.")); + cl::desc("Lower bound for a buffer to be considered for " + "stack protection")); namespace { class VISIBILITY_HIDDEN StackProtector : public FunctionPass { @@ -87,6 +87,41 @@ bool StackProtector::runOnFunction(Function &Fn) { return InsertStackProtectors(); } +/// RequiresStackProtector - Check whether or not this function needs a stack +/// protector based upon the stack protector level. The heuristic we use is to +/// add a guard variable to functions that call alloca, and functions with +/// buffers larger than SSPBufferSize bytes. +bool StackProtector::RequiresStackProtector() const { + if (F->hasFnAttr(Attribute::StackProtectReq)) + return true; + + if (!F->hasFnAttr(Attribute::StackProtect)) + return false; + + const TargetData *TD = TLI->getTargetData(); + + for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) { + BasicBlock *BB = I; + + for (BasicBlock::iterator + II = BB->begin(), IE = BB->end(); II != IE; ++II) + if (AllocaInst *AI = dyn_cast(II)) { + if (AI->isArrayAllocation()) + // This is a call to alloca with a variable size. Emit stack + // protectors. + return true; + + if (const ArrayType *AT = dyn_cast(AI->getAllocatedType())) + // If an array has more than SSPBufferSize bytes of allocated space, + // then we emit stack protectors. + if (SSPBufferSize <= TD->getABITypeSize(AT)) + return true; + } + } + + return false; +} + /// InsertStackProtectors - Insert code into the prologue and epilogue of the /// function. /// @@ -94,77 +129,79 @@ bool StackProtector::runOnFunction(Function &Fn) { /// - The epilogue checks the value stored in the prologue against the original /// value. It calls __stack_chk_fail if they differ. bool StackProtector::InsertStackProtectors() { - // Loop through the basic blocks that have return instructions. Convert this: - // - // return: - // ... - // ret ... - // - // into this: - // - // return: - // ... - // %1 = load __stack_chk_guard - // %2 = load - // %3 = cmp i1 %1, %2 - // br i1 %3, label %SP_return, label %CallStackCheckFailBlk - // - // SP_return: - // ret ... - // - // CallStackCheckFailBlk: - // call void @__stack_chk_fail() - // unreachable - // BasicBlock *FailBB = 0; // The basic block to jump to if check fails. AllocaInst *AI = 0; // Place on stack that stores the stack guard. Constant *StackGuardVar = 0; // The stack guard variable. for (Function::iterator I = F->begin(), E = F->end(); I != E; ) { - BasicBlock *BB = I; - - if (ReturnInst *RI = dyn_cast(BB->getTerminator())) { - if (!FailBB) { - // Insert code into the entry block that stores the __stack_chk_guard - // variable onto the stack. - PointerType *PtrTy = PointerType::getUnqual(Type::Int8Ty); - StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy); - - BasicBlock &Entry = F->getEntryBlock(); - Instruction *InsPt = &Entry.front(); - - AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt); - LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt); - - Value *Args[] = { LI, AI }; - CallInst:: - Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector_create), - &Args[0], array_endof(Args), "", InsPt); - - // Create the basic block to jump to when the guard check fails. - FailBB = CreateFailBB(); - } - - ++I; // Skip to the next block so that we don't resplit the return block. - - // Split the basic block before the return instruction. - BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return"); - - // Move the newly created basic block to the point right after the old - // basic block so that it's in the "fall through" position. - NewBB->removeFromParent(); - F->getBasicBlockList().insert(I, NewBB); - - // Generate the stack protector instructions in the old basic block. - LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB); - CallInst *CI = CallInst:: - Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector_check), - AI, "", BB); - ICmpInst *Cmp = new ICmpInst(CmpInst::ICMP_EQ, CI, LI1, "", BB); - BranchInst::Create(NewBB, FailBB, Cmp, BB); - } else { - ++I; + BasicBlock *BB = I++; + + ReturnInst *RI = dyn_cast(BB->getTerminator()); + if (!RI) continue; + + if (!FailBB) { + // Insert code into the entry block that stores the __stack_chk_guard + // variable onto the stack: + // + // entry: + // StackGuardSlot = alloca i8* + // StackGuard = load __stack_chk_guard + // call void @llvm.stackprotect.create(StackGuard, StackGuardSlot) + // + PointerType *PtrTy = PointerType::getUnqual(Type::Int8Ty); + StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy); + + BasicBlock &Entry = F->getEntryBlock(); + Instruction *InsPt = &Entry.front(); + + AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt); + LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt); + + Value *Args[] = { LI, AI }; + CallInst:: + Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector_create), + &Args[0], array_endof(Args), "", InsPt); + + // Create the basic block to jump to when the guard check fails. + FailBB = CreateFailBB(); } + + // For each block with a return instruction, convert this: + // + // return: + // ... + // ret ... + // + // into this: + // + // return: + // ... + // %1 = load __stack_chk_guard + // %2 = call i8* @llvm.stackprotect.check(StackGuardSlot) + // %3 = cmp i1 %1, %2 + // br i1 %3, label %SP_return, label %CallStackCheckFailBlk + // + // SP_return: + // ret ... + // + // CallStackCheckFailBlk: + // call void @__stack_chk_fail() + // unreachable + + // Split the basic block before the return instruction. + BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return"); + + // Move the newly created basic block to the point right after the old basic + // block so that it's in the "fall through" position. + NewBB->moveAfter(BB); + + // Generate the stack protector instructions in the old basic block. + LoadInst *LI = new LoadInst(StackGuardVar, "", false, BB); + CallInst *CI = CallInst:: + Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector_check), + AI, "", BB); + ICmpInst *Cmp = new ICmpInst(CmpInst::ICMP_EQ, CI, LI, "", BB); + BranchInst::Create(NewBB, FailBB, Cmp, BB); } // Return if we didn't modify any basic blocks. I.e., there are no return @@ -184,39 +221,3 @@ BasicBlock *StackProtector::CreateFailBB() { new UnreachableInst(FailBB); return FailBB; } - -/// RequiresStackProtector - Check whether or not this function needs a stack -/// protector based upon the stack protector level. The heuristic we use is to -/// add a guard variable to functions that call alloca, and functions with -/// buffers larger than 8 bytes. -bool StackProtector::RequiresStackProtector() const { - if (F->hasFnAttr(Attribute::StackProtectReq)) - return true; - - if (F->hasFnAttr(Attribute::StackProtect)) { - const TargetData *TD = TLI->getTargetData(); - - for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) { - BasicBlock *BB = I; - - for (BasicBlock::iterator - II = BB->begin(), IE = BB->end(); II != IE; ++II) - if (AllocaInst *AI = dyn_cast(II)) { - if (AI->isArrayAllocation()) - // This is a call to alloca with a variable size. Emit stack - // protectors. - return true; - - if (const ArrayType *AT = dyn_cast(AI->getAllocatedType())) - // If an array has more than 8 bytes of allocated space, then we - // emit stack protectors. - if (SSPBufferSize <= TD->getABITypeSize(AT)) - return true; - } - } - - return false; - } - - return false; -} -- 2.34.1