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//===- NoopInsertion.cpp - Noop Insertion ---------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass adds fine-grained diversity by displacing code using randomly
// placed (optionally target supplied) Noop instructions.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/NoopInsertion.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/RandomNumberGenerator.h"
#include "llvm/Target/TargetInstrInfo.h"
using namespace llvm;
#define DEBUG_TYPE "noop-insertion"
static cl::opt<unsigned> NoopInsertionPercentage(
"noop-insertion-percentage",
cl::desc("Percentage of instructions that have Noops prepended"),
cl::init(25)); // Default is a good balance between entropy and
// performance impact
static cl::opt<unsigned> MaxNoopsPerInstruction(
"max-noops-per-instruction",
llvm::cl::desc("Maximum number of Noops per instruction"),
llvm::cl::init(1));
STATISTIC(InsertedNoops,
"Total number of noop type instructions inserted for diversity");
char NoopInsertion::ID = 0;
char &llvm::NoopInsertionID = NoopInsertion::ID;
INITIALIZE_PASS(NoopInsertion, "noop-insertion",
"Noop Insertion for fine-grained code randomization", false,
false)
NoopInsertion::NoopInsertion() : MachineFunctionPass(ID) {
initializeNoopInsertionPass(*PassRegistry::getPassRegistry());
// clamp percentage to 100
if (NoopInsertionPercentage > 100)
NoopInsertionPercentage = 100;
}
void NoopInsertion::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool NoopInsertion::runOnMachineFunction(MachineFunction &Fn) {
// The RNG must be initialized on first use so we have a Module to
// construct it from
if (!RNG)
RNG.reset(Fn.getFunction()->getParent()->createRNG(this));
const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
unsigned FnInsertedNoopCount = 0;
for (auto &BB : Fn) {
MachineBasicBlock::iterator FirstTerm = BB.getFirstTerminator();
for (MachineBasicBlock::iterator I = BB.begin(), E = BB.end(); I != E;
++I) {
if (I->isPseudo())
continue;
// Insert random number of Noop-like instructions.
for (unsigned i = 0; i < MaxNoopsPerInstruction; i++) {
if (Distribution(*RNG) >= NoopInsertionPercentage)
continue;
TII->insertNoop(BB, I, *RNG);
++FnInsertedNoopCount;
}
if (I == FirstTerm)
break;
}
}
InsertedNoops += FnInsertedNoopCount;
return FnInsertedNoopCount > 0;
}
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