Fixing issues with alignment, undefined behaviour and endianness in the FieldTrial::HashName functi…

base/metrics/field_trial.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/field_trial.h"
 
 #include "base/build_time.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/sha1.h"
 #include "base/stringprintf.h"
 #include "base/string_util.h"
+#include "base/sys_byteorder.h"
 #include "base/utf_string_conversions.h"
 
 namespace base {
 
 static const char kHistogramFieldTrialSeparator('_');
 
 // statics
 const int FieldTrial::kNotFinalized = -1;
 const int FieldTrial::kDefaultGroupNumber = 0;
 const uint32 FieldTrial::kReservedHashValue = 0;
@@ skipping 182 matching lines @@
 // static
 uint32 FieldTrial::HashName(const std::string& name) {
   // SHA-1 is designed to produce a uniformly random spread in its output space,
   // even for nearly-identical inputs.
   unsigned char sha1_hash[kSHA1Length];
   SHA1HashBytes(reinterpret_cast<const unsigned char*>(name.c_str()),
                 name.size(),
                 sha1_hash);
 
   COMPILE_ASSERT(sizeof(uint32) < sizeof(sha1_hash), need_more_data);
-  uint32* bits = reinterpret_cast<uint32*>(&sha1_hash[0]);
+  uint32 bits;
+  memcpy(&bits, sha1_hash, sizeof(bits));
 
   // We only DCHECK, since this should not happen because the registration
   // of the experiment on the server should have already warn the developer.
   // If this ever happen, we'll ignore this experiment/group when reporting.
-  DCHECK(*bits != kReservedHashValue);
-  return *bits;
+  DCHECK(bits != kReservedHashValue);
+  return base::ByteSwapToLE32(bits);
 }
 
 //------------------------------------------------------------------------------
 // FieldTrialList methods and members.
 
 // static
 FieldTrialList* FieldTrialList::global_ = NULL;
 
 // static
 bool FieldTrialList::used_without_global_ = false;
@@ skipping 244 matching lines @@
     used_without_global_ = true;
     return;
   }
   AutoLock auto_lock(global_->lock_);
   DCHECK(!global_->PreLockedFind(trial->name()));
   trial->AddRef();
   global_->registered_[trial->name()] = trial;
 }
 
 }  // namespace base