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-rw-r--r--lib/Transforms/IPO/LowerBitSets.cpp276
1 files changed, 197 insertions, 79 deletions
diff --git a/lib/Transforms/IPO/LowerBitSets.cpp b/lib/Transforms/IPO/LowerBitSets.cpp
index 0a22a80..fe00d92 100644
--- a/lib/Transforms/IPO/LowerBitSets.cpp
+++ b/lib/Transforms/IPO/LowerBitSets.cpp
@@ -16,6 +16,7 @@
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/Triple.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/GlobalVariable.h"
@@ -31,10 +32,17 @@ using namespace llvm;
#define DEBUG_TYPE "lowerbitsets"
-STATISTIC(NumBitSetsCreated, "Number of bitsets created");
+STATISTIC(ByteArraySizeBits, "Byte array size in bits");
+STATISTIC(ByteArraySizeBytes, "Byte array size in bytes");
+STATISTIC(NumByteArraysCreated, "Number of byte arrays created");
STATISTIC(NumBitSetCallsLowered, "Number of bitset calls lowered");
STATISTIC(NumBitSetDisjointSets, "Number of disjoint sets of bitsets");
+static cl::opt<bool> AvoidReuse(
+ "lowerbitsets-avoid-reuse",
+ cl::desc("Try to avoid reuse of byte array addresses using aliases"),
+ cl::Hidden, cl::init(true));
+
bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const {
if (Offset < ByteOffset)
return false;
@@ -46,11 +54,11 @@ bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const {
if (BitOffset >= BitSize)
return false;
- return (Bits[BitOffset / 8] >> (BitOffset % 8)) & 1;
+ return Bits.count(BitOffset);
}
bool BitSetInfo::containsValue(
- const DataLayout *DL,
+ const DataLayout &DL,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout, Value *V,
uint64_t COffset) const {
if (auto GV = dyn_cast<GlobalVariable>(V)) {
@@ -61,8 +69,8 @@ bool BitSetInfo::containsValue(
}
if (auto GEP = dyn_cast<GEPOperator>(V)) {
- APInt APOffset(DL->getPointerSizeInBits(0), 0);
- bool Result = GEP->accumulateConstantOffset(*DL, APOffset);
+ APInt APOffset(DL.getPointerSizeInBits(0), 0);
+ bool Result = GEP->accumulateConstantOffset(DL, APOffset);
if (!Result)
return false;
COffset += APOffset.getZExtValue();
@@ -101,18 +109,15 @@ BitSetInfo BitSetBuilder::build() {
BSI.ByteOffset = Min;
BSI.AlignLog2 = 0;
- // FIXME: Can probably do something smarter if all offsets are 0.
if (Mask != 0)
BSI.AlignLog2 = countTrailingZeros(Mask, ZB_Undefined);
// Build the compressed bitset while normalizing the offsets against the
// computed alignment.
BSI.BitSize = ((Max - Min) >> BSI.AlignLog2) + 1;
- uint64_t ByteSize = (BSI.BitSize + 7) / 8;
- BSI.Bits.resize(ByteSize);
for (uint64_t Offset : Offsets) {
Offset >>= BSI.AlignLog2;
- BSI.Bits[Offset / 8] |= 1 << (Offset % 8);
+ BSI.Bits.insert(Offset);
}
return BSI;
@@ -147,15 +152,47 @@ void GlobalLayoutBuilder::addFragment(const std::set<uint64_t> &F) {
FragmentMap[ObjIndex] = FragmentIndex;
}
+void ByteArrayBuilder::allocate(const std::set<uint64_t> &Bits,
+ uint64_t BitSize, uint64_t &AllocByteOffset,
+ uint8_t &AllocMask) {
+ // Find the smallest current allocation.
+ unsigned Bit = 0;
+ for (unsigned I = 1; I != BitsPerByte; ++I)
+ if (BitAllocs[I] < BitAllocs[Bit])
+ Bit = I;
+
+ AllocByteOffset = BitAllocs[Bit];
+
+ // Add our size to it.
+ unsigned ReqSize = AllocByteOffset + BitSize;
+ BitAllocs[Bit] = ReqSize;
+ if (Bytes.size() < ReqSize)
+ Bytes.resize(ReqSize);
+
+ // Set our bits.
+ AllocMask = 1 << Bit;
+ for (uint64_t B : Bits)
+ Bytes[AllocByteOffset + B] |= AllocMask;
+}
+
namespace {
+struct ByteArrayInfo {
+ std::set<uint64_t> Bits;
+ uint64_t BitSize;
+ GlobalVariable *ByteArray;
+ Constant *Mask;
+};
+
struct LowerBitSets : public ModulePass {
static char ID;
LowerBitSets() : ModulePass(ID) {
initializeLowerBitSetsPass(*PassRegistry::getPassRegistry());
}
- const DataLayout *DL;
+ Module *M;
+
+ bool LinkerSubsectionsViaSymbols;
IntegerType *Int1Ty;
IntegerType *Int8Ty;
IntegerType *Int32Ty;
@@ -169,20 +206,23 @@ struct LowerBitSets : public ModulePass {
// Mapping from bitset mdstrings to the call sites that test them.
DenseMap<MDString *, std::vector<CallInst *>> BitSetTestCallSites;
+ std::vector<ByteArrayInfo> ByteArrayInfos;
+
BitSetInfo
buildBitSet(MDString *BitSet,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
- Value *createBitSetTest(IRBuilder<> &B, const BitSetInfo &BSI,
- GlobalVariable *BitSetGlobal, Value *BitOffset);
+ ByteArrayInfo *createByteArray(BitSetInfo &BSI);
+ void allocateByteArrays();
+ Value *createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI, ByteArrayInfo *&BAI,
+ Value *BitOffset);
Value *
- lowerBitSetCall(CallInst *CI, const BitSetInfo &BSI,
- GlobalVariable *BitSetGlobal, GlobalVariable *CombinedGlobal,
+ lowerBitSetCall(CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
+ GlobalVariable *CombinedGlobal,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
- void buildBitSetsFromGlobals(Module &M,
- const std::vector<MDString *> &BitSets,
+ void buildBitSetsFromGlobals(const std::vector<MDString *> &BitSets,
const std::vector<GlobalVariable *> &Globals);
- bool buildBitSets(Module &M);
- bool eraseBitSetMetadata(Module &M);
+ bool buildBitSets();
+ bool eraseBitSetMetadata();
bool doInitialization(Module &M) override;
bool runOnModule(Module &M) override;
@@ -198,19 +238,21 @@ char LowerBitSets::ID = 0;
ModulePass *llvm::createLowerBitSetsPass() { return new LowerBitSets; }
-bool LowerBitSets::doInitialization(Module &M) {
- DL = M.getDataLayout();
- if (!DL)
- report_fatal_error("Data layout required");
+bool LowerBitSets::doInitialization(Module &Mod) {
+ M = &Mod;
+ const DataLayout &DL = Mod.getDataLayout();
- Int1Ty = Type::getInt1Ty(M.getContext());
- Int8Ty = Type::getInt8Ty(M.getContext());
- Int32Ty = Type::getInt32Ty(M.getContext());
+ Triple TargetTriple(M->getTargetTriple());
+ LinkerSubsectionsViaSymbols = TargetTriple.isMacOSX();
+
+ Int1Ty = Type::getInt1Ty(M->getContext());
+ Int8Ty = Type::getInt8Ty(M->getContext());
+ Int32Ty = Type::getInt32Ty(M->getContext());
Int32PtrTy = PointerType::getUnqual(Int32Ty);
- Int64Ty = Type::getInt64Ty(M.getContext());
- IntPtrTy = DL->getIntPtrType(M.getContext(), 0);
+ Int64Ty = Type::getInt64Ty(M->getContext());
+ IntPtrTy = DL.getIntPtrType(M->getContext(), 0);
- BitSetNM = M.getNamedMetadata("llvm.bitsets");
+ BitSetNM = M->getNamedMetadata("llvm.bitsets");
BitSetTestCallSites.clear();
@@ -259,52 +301,128 @@ static Value *createMaskedBitTest(IRBuilder<> &B, Value *Bits,
return B.CreateICmpNE(MaskedBits, ConstantInt::get(BitsType, 0));
}
+ByteArrayInfo *LowerBitSets::createByteArray(BitSetInfo &BSI) {
+ // Create globals to stand in for byte arrays and masks. These never actually
+ // get initialized, we RAUW and erase them later in allocateByteArrays() once
+ // we know the offset and mask to use.
+ auto ByteArrayGlobal = new GlobalVariable(
+ *M, Int8Ty, /*isConstant=*/true, GlobalValue::PrivateLinkage, nullptr);
+ auto MaskGlobal = new GlobalVariable(
+ *M, Int8Ty, /*isConstant=*/true, GlobalValue::PrivateLinkage, nullptr);
+
+ ByteArrayInfos.emplace_back();
+ ByteArrayInfo *BAI = &ByteArrayInfos.back();
+
+ BAI->Bits = BSI.Bits;
+ BAI->BitSize = BSI.BitSize;
+ BAI->ByteArray = ByteArrayGlobal;
+ BAI->Mask = ConstantExpr::getPtrToInt(MaskGlobal, Int8Ty);
+ return BAI;
+}
+
+void LowerBitSets::allocateByteArrays() {
+ std::stable_sort(ByteArrayInfos.begin(), ByteArrayInfos.end(),
+ [](const ByteArrayInfo &BAI1, const ByteArrayInfo &BAI2) {
+ return BAI1.BitSize > BAI2.BitSize;
+ });
+
+ std::vector<uint64_t> ByteArrayOffsets(ByteArrayInfos.size());
+
+ ByteArrayBuilder BAB;
+ for (unsigned I = 0; I != ByteArrayInfos.size(); ++I) {
+ ByteArrayInfo *BAI = &ByteArrayInfos[I];
+
+ uint8_t Mask;
+ BAB.allocate(BAI->Bits, BAI->BitSize, ByteArrayOffsets[I], Mask);
+
+ BAI->Mask->replaceAllUsesWith(ConstantInt::get(Int8Ty, Mask));
+ cast<GlobalVariable>(BAI->Mask->getOperand(0))->eraseFromParent();
+ }
+
+ Constant *ByteArrayConst = ConstantDataArray::get(M->getContext(), BAB.Bytes);
+ auto ByteArray =
+ new GlobalVariable(*M, ByteArrayConst->getType(), /*isConstant=*/true,
+ GlobalValue::PrivateLinkage, ByteArrayConst);
+
+ for (unsigned I = 0; I != ByteArrayInfos.size(); ++I) {
+ ByteArrayInfo *BAI = &ByteArrayInfos[I];
+
+ Constant *Idxs[] = {ConstantInt::get(IntPtrTy, 0),
+ ConstantInt::get(IntPtrTy, ByteArrayOffsets[I])};
+ Constant *GEP = ConstantExpr::getInBoundsGetElementPtr(ByteArray, Idxs);
+
+ // Create an alias instead of RAUW'ing the gep directly. On x86 this ensures
+ // that the pc-relative displacement is folded into the lea instead of the
+ // test instruction getting another displacement.
+ if (LinkerSubsectionsViaSymbols) {
+ BAI->ByteArray->replaceAllUsesWith(GEP);
+ } else {
+ GlobalAlias *Alias = GlobalAlias::create(
+ Int8Ty, 0, GlobalValue::PrivateLinkage, "bits", GEP, M);
+ BAI->ByteArray->replaceAllUsesWith(Alias);
+ }
+ BAI->ByteArray->eraseFromParent();
+ }
+
+ ByteArraySizeBits = BAB.BitAllocs[0] + BAB.BitAllocs[1] + BAB.BitAllocs[2] +
+ BAB.BitAllocs[3] + BAB.BitAllocs[4] + BAB.BitAllocs[5] +
+ BAB.BitAllocs[6] + BAB.BitAllocs[7];
+ ByteArraySizeBytes = BAB.Bytes.size();
+}
+
/// Build a test that bit BitOffset is set in BSI, where
/// BitSetGlobal is a global containing the bits in BSI.
-Value *LowerBitSets::createBitSetTest(IRBuilder<> &B, const BitSetInfo &BSI,
- GlobalVariable *BitSetGlobal,
- Value *BitOffset) {
- if (BSI.Bits.size() <= 8) {
+Value *LowerBitSets::createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI,
+ ByteArrayInfo *&BAI, Value *BitOffset) {
+ if (BSI.BitSize <= 64) {
// If the bit set is sufficiently small, we can avoid a load by bit testing
// a constant.
IntegerType *BitsTy;
- if (BSI.Bits.size() <= 4)
+ if (BSI.BitSize <= 32)
BitsTy = Int32Ty;
else
BitsTy = Int64Ty;
uint64_t Bits = 0;
- for (auto I = BSI.Bits.rbegin(), E = BSI.Bits.rend(); I != E; ++I) {
- Bits <<= 8;
- Bits |= *I;
- }
+ for (auto Bit : BSI.Bits)
+ Bits |= uint64_t(1) << Bit;
Constant *BitsConst = ConstantInt::get(BitsTy, Bits);
return createMaskedBitTest(B, BitsConst, BitOffset);
} else {
- // TODO: We might want to use the memory variant of the bt instruction
- // with the previously computed bit offset at -Os. This instruction does
- // exactly what we want but has been benchmarked as being slower than open
- // coding the load+bt.
- Value *BitSetGlobalOffset =
- B.CreateLShr(BitOffset, ConstantInt::get(IntPtrTy, 5));
- Value *BitSetEntryAddr = B.CreateGEP(
- ConstantExpr::getBitCast(BitSetGlobal, Int32PtrTy), BitSetGlobalOffset);
- Value *BitSetEntry = B.CreateLoad(BitSetEntryAddr);
-
- return createMaskedBitTest(B, BitSetEntry, BitOffset);
+ if (!BAI) {
+ ++NumByteArraysCreated;
+ BAI = createByteArray(BSI);
+ }
+
+ Constant *ByteArray = BAI->ByteArray;
+ if (!LinkerSubsectionsViaSymbols && AvoidReuse) {
+ // Each use of the byte array uses a different alias. This makes the
+ // backend less likely to reuse previously computed byte array addresses,
+ // improving the security of the CFI mechanism based on this pass.
+ ByteArray = GlobalAlias::create(
+ BAI->ByteArray->getType()->getElementType(), 0,
+ GlobalValue::PrivateLinkage, "bits_use", ByteArray, M);
+ }
+
+ Value *ByteAddr = B.CreateGEP(ByteArray, BitOffset);
+ Value *Byte = B.CreateLoad(ByteAddr);
+
+ Value *ByteAndMask = B.CreateAnd(Byte, BAI->Mask);
+ return B.CreateICmpNE(ByteAndMask, ConstantInt::get(Int8Ty, 0));
}
}
/// Lower a llvm.bitset.test call to its implementation. Returns the value to
/// replace the call with.
Value *LowerBitSets::lowerBitSetCall(
- CallInst *CI, const BitSetInfo &BSI, GlobalVariable *BitSetGlobal,
+ CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
GlobalVariable *CombinedGlobal,
const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
Value *Ptr = CI->getArgOperand(0);
+ const DataLayout &DL = M->getDataLayout();
if (BSI.containsValue(DL, GlobalLayout, Ptr))
- return ConstantInt::getTrue(BitSetGlobal->getParent()->getContext());
+ return ConstantInt::getTrue(CombinedGlobal->getParent()->getContext());
Constant *GlobalAsInt = ConstantExpr::getPtrToInt(CombinedGlobal, IntPtrTy);
Constant *OffsetedGlobalAsInt = ConstantExpr::getAdd(
@@ -336,8 +454,8 @@ Value *LowerBitSets::lowerBitSetCall(
Value *OffsetSHR =
B.CreateLShr(PtrOffset, ConstantInt::get(IntPtrTy, BSI.AlignLog2));
Value *OffsetSHL = B.CreateShl(
- PtrOffset, ConstantInt::get(IntPtrTy, DL->getPointerSizeInBits(0) -
- BSI.AlignLog2));
+ PtrOffset,
+ ConstantInt::get(IntPtrTy, DL.getPointerSizeInBits(0) - BSI.AlignLog2));
BitOffset = B.CreateOr(OffsetSHR, OffsetSHL);
}
@@ -353,7 +471,7 @@ Value *LowerBitSets::lowerBitSetCall(
// Now that we know that the offset is in range and aligned, load the
// appropriate bit from the bitset.
- Value *Bit = createBitSetTest(ThenB, BSI, BitSetGlobal, BitOffset);
+ Value *Bit = createBitSetTest(ThenB, BSI, BAI, BitOffset);
// The value we want is 0 if we came directly from the initial block
// (having failed the range or alignment checks), or the loaded bit if
@@ -368,14 +486,14 @@ Value *LowerBitSets::lowerBitSetCall(
/// Given a disjoint set of bitsets and globals, layout the globals, build the
/// bit sets and lower the llvm.bitset.test calls.
void LowerBitSets::buildBitSetsFromGlobals(
- Module &M,
const std::vector<MDString *> &BitSets,
const std::vector<GlobalVariable *> &Globals) {
// Build a new global with the combined contents of the referenced globals.
std::vector<Constant *> GlobalInits;
+ const DataLayout &DL = M->getDataLayout();
for (GlobalVariable *G : Globals) {
GlobalInits.push_back(G->getInitializer());
- uint64_t InitSize = DL->getTypeAllocSize(G->getInitializer()->getType());
+ uint64_t InitSize = DL.getTypeAllocSize(G->getInitializer()->getType());
// Compute the amount of padding required to align the next element to the
// next power of 2.
@@ -391,13 +509,13 @@ void LowerBitSets::buildBitSetsFromGlobals(
}
if (!GlobalInits.empty())
GlobalInits.pop_back();
- Constant *NewInit = ConstantStruct::getAnon(M.getContext(), GlobalInits);
+ Constant *NewInit = ConstantStruct::getAnon(M->getContext(), GlobalInits);
auto CombinedGlobal =
- new GlobalVariable(M, NewInit->getType(), /*isConstant=*/true,
+ new GlobalVariable(*M, NewInit->getType(), /*isConstant=*/true,
GlobalValue::PrivateLinkage, NewInit);
const StructLayout *CombinedGlobalLayout =
- DL->getStructLayout(cast<StructType>(NewInit->getType()));
+ DL.getStructLayout(cast<StructType>(NewInit->getType()));
// Compute the offsets of the original globals within the new global.
DenseMap<GlobalVariable *, uint64_t> GlobalLayout;
@@ -410,18 +528,12 @@ void LowerBitSets::buildBitSetsFromGlobals(
// Build the bitset.
BitSetInfo BSI = buildBitSet(BS, GlobalLayout);
- // Create a global in which to store it.
- ++NumBitSetsCreated;
- Constant *BitsConst = ConstantDataArray::get(M.getContext(), BSI.Bits);
- auto BitSetGlobal = new GlobalVariable(
- M, BitsConst->getType(), /*isConstant=*/true,
- GlobalValue::PrivateLinkage, BitsConst, BS->getString() + ".bits");
+ ByteArrayInfo *BAI = 0;
// Lower each call to llvm.bitset.test for this bitset.
for (CallInst *CI : BitSetTestCallSites[BS]) {
++NumBitSetCallsLowered;
- Value *Lowered =
- lowerBitSetCall(CI, BSI, BitSetGlobal, CombinedGlobal, GlobalLayout);
+ Value *Lowered = lowerBitSetCall(CI, BSI, BAI, CombinedGlobal, GlobalLayout);
CI->replaceAllUsesWith(Lowered);
CI->eraseFromParent();
}
@@ -436,20 +548,24 @@ void LowerBitSets::buildBitSetsFromGlobals(
ConstantInt::get(Int32Ty, I * 2)};
Constant *CombinedGlobalElemPtr =
ConstantExpr::getGetElementPtr(CombinedGlobal, CombinedGlobalIdxs);
- GlobalAlias *GAlias = GlobalAlias::create(
- Globals[I]->getType()->getElementType(),
- Globals[I]->getType()->getAddressSpace(), Globals[I]->getLinkage(),
- "", CombinedGlobalElemPtr, &M);
- GAlias->takeName(Globals[I]);
- Globals[I]->replaceAllUsesWith(GAlias);
+ if (LinkerSubsectionsViaSymbols) {
+ Globals[I]->replaceAllUsesWith(CombinedGlobalElemPtr);
+ } else {
+ GlobalAlias *GAlias = GlobalAlias::create(
+ Globals[I]->getType()->getElementType(),
+ Globals[I]->getType()->getAddressSpace(), Globals[I]->getLinkage(),
+ "", CombinedGlobalElemPtr, M);
+ GAlias->takeName(Globals[I]);
+ Globals[I]->replaceAllUsesWith(GAlias);
+ }
Globals[I]->eraseFromParent();
}
}
/// Lower all bit sets in this module.
-bool LowerBitSets::buildBitSets(Module &M) {
+bool LowerBitSets::buildBitSets() {
Function *BitSetTestFunc =
- M.getFunction(Intrinsic::getName(Intrinsic::bitset_test));
+ M->getFunction(Intrinsic::getName(Intrinsic::bitset_test));
if (!BitSetTestFunc)
return false;
@@ -591,22 +707,24 @@ bool LowerBitSets::buildBitSets(Module &M) {
});
// Build the bitsets from this disjoint set.
- buildBitSetsFromGlobals(M, BitSets, OrderedGlobals);
+ buildBitSetsFromGlobals(BitSets, OrderedGlobals);
}
+ allocateByteArrays();
+
return true;
}
-bool LowerBitSets::eraseBitSetMetadata(Module &M) {
+bool LowerBitSets::eraseBitSetMetadata() {
if (!BitSetNM)
return false;
- M.eraseNamedMetadata(BitSetNM);
+ M->eraseNamedMetadata(BitSetNM);
return true;
}
bool LowerBitSets::runOnModule(Module &M) {
- bool Changed = buildBitSets(M);
- Changed |= eraseBitSetMetadata(M);
+ bool Changed = buildBitSets();
+ Changed |= eraseBitSetMetadata();
return Changed;
}
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