Create one-off tool pnacl-hack-memset

tools/pnacl-hack-memset/pnacl-hack-memset.cpp

+/* Copyright 2016 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can
+ * be found in the LICENSE file.
+ */
+
+//===-- pnacl-hack-memset.cpp - Fix (interim) Subzero bug -----------------===//
+//
+//===----------------------------------------------------------------------===//
+//
+// Fixes generated pexe's so that a Subzero bug (fixed but not yet fully
+// deployed until 10/2016). Does this by replacing calls to memset with a
+// constant (negative) byte value, and corresponding constant count arguments,
+// with a zero-add to the count. This causes the broken (and fixed) optimization
+// to not be fired.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Bitcode/NaCl/NaClReaderWriter.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/DataStream.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/PrettyStackTrace.h"
+#include "llvm/Support/Signals.h"
+#include "llvm/Support/StreamingMemoryObject.h"
+#include "llvm/Support/ToolOutputFile.h"
+
+using namespace llvm;
+
+namespace {
+
+cl::opt<std::string>
+OutputFilename("o", cl::desc("Specify fixed pexe filename"),
+               cl::value_desc("fixed pexe file"), cl::init("-"));
+
+cl::opt<std::string>
+InputFilename(cl::Positional, cl::desc("<pexe file>"), cl::init("-"));
+
+cl::opt<bool>
+ShowFixes("show-fixes", cl::desc("Show fixes to memset"), cl::init(false));
+
+void WriteOutputFile(const Module *M) {
+
+  std::error_code EC;
+  std::unique_ptr<tool_output_file> Out(
+      new tool_output_file(OutputFilename, EC, sys::fs::F_None));
+  if (EC) {
+    errs() << EC.message() << '\n';
+    exit(1);
+  }
+
+  NaClWriteBitcodeToFile(M, Out->os(), /* AcceptSupportedOnly = */ false);
+
+  // Declare success.
+  Out->keep();
+}
+
+Module *readBitcode(std::string &Filename, LLVMContext &Context,
+                    std::string &ErrorMessage) {
+  // Use the bitcode streaming interface
+  DataStreamer *Streamer = getDataFileStreamer(InputFilename, &ErrorMessage);
+  if (Streamer == nullptr)
+    return nullptr;
+  std::unique_ptr<StreamingMemoryObject> Buffer(
+      new StreamingMemoryObjectImpl(Streamer));
+  std::string DisplayFilename;
+  if (Filename == "-")
+    DisplayFilename = "<stdin>";
+  else
+    DisplayFilename = Filename;
+  DiagnosticHandlerFunction DiagnosticHandler = nullptr;
+  Module *M = getNaClStreamedBitcodeModule(
+      DisplayFilename, Buffer.release(), Context, DiagnosticHandler,
+      &ErrorMessage, /*AcceptSupportedOnly=*/false);
+  if (!M)
+    return nullptr;
+  if (std::error_code EC = M->materializeAllPermanently()) {
+    ErrorMessage = EC.message();
+    delete M;
+    return nullptr;
+  }
+  return M;
+}
+
+// Fixes the memset call if appropriate.  Returns 1 if the Call to memset has
+// been fixed, and zero otherwise.
+size_t fixCallToMemset(CallInst *Call) {
+  if (Call->getNumArgOperands() != 5)
+    return 0;
+  Value *Val = Call->getArgOperand(1);
+  auto *CVal = dyn_cast<ConstantInt>(Val);
+  if (CVal == nullptr)
+    return 0;
+  if (!CVal->getType()->isIntegerTy(8))
+    return 0;
+  const APInt &IVal = CVal->getUniqueInteger();
+  if (!IVal.isNegative())
+    return 0;
+  Value *Count = Call->getArgOperand(2);
+  auto *CCount = dyn_cast<ConstantInt>(Count);
+  if (CCount == nullptr)
+    return 0;
+  if (!CCount->getType()->isIntegerTy(32))
+    return 0;
+  if (ShowFixes) {
+    Call->print(errs());
+    errs() << "\n-->\n";
+  }
+  auto *Zero = ConstantInt::getSigned(CCount->getType(), 0);
+  auto *Add = BinaryOperator::Create(Instruction::BinaryOps::Add, CCount, Zero);
+  auto *IAdd = dyn_cast<Instruction>(Add);
+  if (IAdd == nullptr)
+    return 0;
+  Call->setArgOperand(2, Add);
+  IAdd->insertBefore(Call);
+  if (ShowFixes) {
+    IAdd->print(errs());
+    errs() << "\n";
+    Call->print(errs());
+    errs() << "\n\n";
+  }
+  return 1;
+}
+
+// Fixes the instruction Inst, if it is a memset call that needs to be fixed.
+// Returns 1 if the instruction Inst has been fixed, and zero otherwise.
+size_t fixCallToMemset(Instruction *Inst) {
+  size_t Count = 0;
+  if (auto *Call = dyn_cast<CallInst>(Inst)) {
+    if (Function *Fcn = Call->getCalledFunction()) {
+      if ("llvm.memset.p0i8.i32" == Fcn->getName()) {
+        Count += fixCallToMemset(Call);
+      }
+    }
+  }
+  return Count;
+}
+
+// Fixes appropriate memset calls in the basic Block.  Returns the number of
+// fixed memset calls in the given basic Block.
+size_t fixCallsToMemset(BasicBlock *Block) {
+  size_t Count = 0;
+  for (auto &Inst : *Block) {
+    Count += fixCallToMemset(&Inst);
+  }
+  return Count;
+}
+
+// Fixes appropriate memset calls in the function Fcn.  Returns the number of
+// fixed memset calls for the given function.
+size_t fixCallsToMemset(Function *Fcn) {
+  size_t Count = 0;
+  for (auto &Block : *Fcn) {
+    Count += fixCallsToMemset(&Block);
+  }
+  return Count;
+}
+
+// Fixes appropriate memset calls in module M> Returns the number of fixed
+// memset calls.
+size_t fixCallsToMemset(Module *M) {
+  size_t ErrorCount = 0;
+  for (auto &Fcn : *M) {
+    if (!Fcn.isDeclaration())
+      ErrorCount += fixCallsToMemset(&Fcn);
+  }
+  return ErrorCount;
+}
+
+} // end of anonymous namespace
+
+int main(int argc, char **argv) {
+  // Print a stack trace if we signal out.
+  sys::PrintStackTraceOnErrorSignal();
+  PrettyStackTraceProgram X(argc, argv);
+
+  LLVMContext &Context = getGlobalContext();
+  llvm_shutdown_obj Y;  // Call llvm_shutdown() on exit.
+
+  cl::ParseCommandLineOptions(
+      argc, argv, "Converts NaCl pexe wire format into LLVM bitcode format\n");
+
+  std::string ErrorMessage;
+  std::unique_ptr<Module> M(readBitcode(InputFilename, Context, ErrorMessage));
+
+  if (!M.get()) {
+    errs() << argv[0] << ": ";
+    if (ErrorMessage.size())
+      errs() << ErrorMessage << "\n";
+    else
+      errs() << "bitcode didn't read correctly.\n";
+    return 1;
+  }
+
+  size_t ErrorCount = fixCallsToMemset(M.get());
+  if (ErrorCount > 0) {
+    errs() << argv[0] << ": Fixed " << ErrorCount << " calls to memset.\n";
+  }
+
+  WriteOutputFile(M.get());
+  return 0;
+}