Add a Fuzzer library

Summary:
A simple genetic in-process coverage-guided fuzz testing library.

I've used this fuzzer to test clang-format
(it found 12+ bugs, thanks djasper@ for the fixes!)
and it may also help us test other parts of LLVM.
So why not keep it in the LLVM repository?

I plan to add the cmake build rules later (in a separate patch, if that's ok)
and also add a clang-format-fuzzer target.

See README.txt for details.

Test Plan: Tests will follow separately.

Reviewers: djasper, chandlerc, rnk

Reviewed By: rnk

Subscribers: majnemer, ygribov, dblaikie, llvm-commits

Differential Revision: http://reviews.llvm.org/D7184

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227252 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Fuzzer/FuzzerUtil.cpp

@@ -0,0 +1,61 @@
+//===- FuzzerUtil.cpp - Misc utils ----------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// Misc utils.
+//===----------------------------------------------------------------------===//
+
+#include "FuzzerInternal.h"
+#include <iostream>
+#include <sys/time.h>
+#include <cassert>
+#include <cstring>
+#include <signal.h>
+
+namespace fuzzer {
+
+void Print(const Unit &v, const char *PrintAfter) {
+  std::cerr << v.size() << ": ";
+  for (auto x : v)
+    std::cerr << (unsigned) x << " ";
+  std::cerr << PrintAfter;
+}
+
+void PrintASCII(const Unit &U, const char *PrintAfter) {
+  for (auto X : U)
+    std::cerr << (char)((isascii(X) && X >= ' ') ? X : '?');
+  std::cerr << PrintAfter;
+}
+
+std::string Hash(const Unit &in) {
+  size_t h1 = 0, h2 = 0;
+  for (auto x : in) {
+    h1 += x;
+    h1 *= 5;
+    h2 += x;
+    h2 *= 7;
+  }
+  return std::to_string(h1) + std::to_string(h2);
+}
+
+static void AlarmHandler(int, siginfo_t *, void *) {
+  Fuzzer::AlarmCallback();
+}
+
+void SetTimer(int Seconds) {
+  struct itimerval T {{Seconds, 0}, {Seconds, 0}};
+  std::cerr << "SetTimer " << Seconds << "\n";
+  int Res = setitimer(ITIMER_REAL, &T, nullptr);
+  assert(Res == 0);
+  struct sigaction sigact;
+  memset(&sigact, 0, sizeof(sigact));
+  sigact.sa_sigaction = AlarmHandler;
+  Res = sigaction(SIGALRM, &sigact, 0);
+  assert(Res == 0);
+}
+
+}  // namespace fuzzer