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- Use "moveAfter" instead of "remove/insert" of a basic block.

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- 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
This commit is contained in:
Bill Wendling 2008-11-18 05:32:11 +00:00
parent 6c2fe2237b
commit c3348a77f7
1 changed files with 98 additions and 97 deletions
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195
lib/CodeGen/StackProtector.cpp
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@ -33,8 +33,8 @@ using namespace llvm;
// smashing protection.
static cl::opt<unsigned>
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<AllocaInst>(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<ArrayType>(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 <stored stack guard>
// %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;
BasicBlock *BB = I++;
if (ReturnInst *RI = dyn_cast<ReturnInst>(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);
ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
if (!RI) continue;
BasicBlock &Entry = F->getEntryBlock();
Instruction *InsPt = &Entry.front();
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);
AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
BasicBlock &Entry = F->getEntryBlock();
Instruction *InsPt = &Entry.front();
Value *Args[] = { LI, AI };
CallInst::
Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector_create),
&Args[0], array_endof(Args), "", InsPt);
AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
// Create the basic block to jump to when the guard check fails.
FailBB = CreateFailBB();
}
Value *Args[] = { LI, AI };
CallInst::
Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector_create),
&Args[0], array_endof(Args), "", InsPt);
++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;
// 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<AllocaInst>(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<ArrayType>(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;
}