Rebased PNaCl localmods in LLVM to 223109

lib/Transforms/MinSFI/SubstituteUndefs.cpp

+//===- SubstituteUndefs.cpp - Replace undefs with deterministic constants -===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// PNaCl bitcode may contain undefined values inside function bodies, i.e. as
+// a placeholder for numerical constants and constant vectors. Their actual
+// value at runtime will most likely be the current value from one of the
+// registers or from the native stack.
+//
+// Using undefined values, the sandboxed code could obtain protected values,
+// such as the base address of the address subspace or a value from another
+// protection domain left in the register file. Additionally, undefined values
+// may introduce undesirable non-determinism.
+//
+// This pass therefore substitutes all undefined expressions with predefined
+// constants.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Pass.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/Transforms/MinSFI.h"
+
+using namespace llvm;
+
+static const uint64_t SubstInt = 0xBAADF00DCAFEBABE;
+static const double SubstFloat = 3.14159265359;
+
+namespace {
+class SubstituteUndefs : public FunctionPass {
+ public:
+  static char ID;
+  SubstituteUndefs() : FunctionPass(ID) {
+    initializeSubstituteUndefsPass(*PassRegistry::getPassRegistry());
+  }
+
+  virtual bool runOnFunction(Function &Func);
+};
+}  // namespace
+
+static inline bool isScalarOrVectorInteger(Type *T) {
+  if (T->isIntegerTy())
+    return true;
+  else if (T->isVectorTy() && T->getVectorElementType()->isIntegerTy())
+    return true;
+  else
+    return false;
+}
+
+static inline bool isScalarOrVectorFloatingPoint(Type *T) {
+  if (T->isFloatingPointTy())
+    return true;
+  else if (T->isVectorTy() && T->getVectorElementType()->isFloatingPointTy())
+    return true;
+  else
+    return false;
+}
+
+bool SubstituteUndefs::runOnFunction(Function &Func) {
+  bool HadUndefs = false;
+  for (Function::iterator BB = Func.begin(), E = Func.end(); BB != E; ++BB) {
+    for (BasicBlock::iterator Inst = BB->begin(), E = BB->end(); Inst != E;
+         ++Inst) {
+      for (int Index = 0, NumOps = Inst->getNumOperands(); Index < NumOps;
+           ++Index) {
+        Value *Operand = Inst->getOperand(Index);
+        if (isa<UndefValue>(Operand)) {
+          HadUndefs = true;
+          Type *OpType = Operand->getType();
+          if (isScalarOrVectorInteger(OpType))
+            Inst->setOperand(Index, ConstantInt::get(OpType, SubstInt));
+          else if (isScalarOrVectorFloatingPoint(OpType))
+            Inst->setOperand(Index, ConstantFP::get(OpType, SubstFloat));
+          else
+            assert(false && "Type of undef not permitted by the PNaCl ABI");
+        }
+      }
+    }
+  }
+  return HadUndefs;
+}
+
+char SubstituteUndefs::ID = 0;
+INITIALIZE_PASS(SubstituteUndefs, "minsfi-substitute-undefs",
+                "Replace undef values with deterministic constants",
+                false, false)
+
+FunctionPass *llvm::createSubstituteUndefsPass() {
+  return new SubstituteUndefs();
+}