Validate checksum calculations.

Crash reports indicate that checksums are valid even though the bucket
boundary values are tested to be incorrect. Try to determine if it is
memory corruption or bad calculations.

Bug: 836238
Change-Id: Ie89df5fef5093e9dd8c45fe9ff26a0430838769e
Reviewed-on: https://chromium-review.googlesource.com/c/1264036Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597194}

base/metrics/bucket_ranges.cc

@@ -74,7 +74,8 @@ const uint32_t kCrcTable[256] = {
 // the CRC correct for big-endian vs little-ending calculations.  All we need is
 // a nice hash, that tends to depend on all the bits of the sample, with very
 // little chance of changes in one place impacting changes in another place.
-static uint32_t Crc32(uint32_t sum, HistogramBase::Sample value) {
+// Temporary non-static for https://crbug.com/836238
+/*static*/ uint32_t Crc32(uint32_t sum, HistogramBase::Sample value) {
   union {
     HistogramBase::Sample range;
     unsigned char bytes[sizeof(HistogramBase::Sample)];

base/metrics/bucket_ranges.h

@@ -99,6 +99,7 @@ class BASE_EXPORT BucketRanges {
 //////////////////////////////////////////////////////////////////////////////
 // Expose only for test.
 BASE_EXPORT extern const uint32_t kCrcTable[256];
+uint32_t Crc32(uint32_t sum, HistogramBase::Sample value);
 
 }  // namespace base
 

base/metrics/histogram.cc

@@ -465,6 +465,16 @@ void Histogram::InitializeBucketRanges(Sample minimum,
   Sample current = minimum;
   ranges->set_range(bucket_index, current);
   size_t bucket_count = ranges->bucket_count();
+
+  // Temporary for https://crbug.com/836238
+  uint32_t checksum = static_cast<uint32_t>(bucket_count + 1);
+  checksum = Crc32(checksum, 0);
+  checksum = Crc32(checksum, current);
+  debug::Alias(&minimum);
+  debug::Alias(&maximum);
+  debug::Alias(&bucket_count);
+  debug::Alias(&checksum);
+
   while (bucket_count > ++bucket_index) {
     double log_current;
     log_current = log(static_cast<double>(current));
@@ -479,9 +489,12 @@ void Histogram::InitializeBucketRanges(Sample minimum,
     else
       ++current;  // Just do a narrow bucket, and keep trying.
     ranges->set_range(bucket_index, current);
+    checksum = Crc32(checksum, current);
   }
   ranges->set_range(ranges->bucket_count(), HistogramBase::kSampleType_MAX);
   ranges->ResetChecksum();
+  checksum = Crc32(checksum, HistogramBase::kSampleType_MAX);
+  CHECK_EQ(checksum, ranges->checksum());
 }
 
 // static
@@ -1094,7 +1107,7 @@ double LinearHistogram::GetBucketSize(Count current, uint32_t i) const {
 
 const std::string LinearHistogram::GetAsciiBucketRange(uint32_t i) const {
   int range = ranges(i);
-  auto it = bucket_description_.find(range);
+  BucketDescriptionMap::const_iterator it = bucket_description_.find(range);
   if (it == bucket_description_.end())
     return Histogram::GetAsciiBucketRange(i);
   return it->second;
@@ -1111,13 +1124,33 @@ void LinearHistogram::InitializeBucketRanges(Sample minimum,
   double min = minimum;
   double max = maximum;
   size_t bucket_count = ranges->bucket_count();
+
+  // Temporary for https://crbug.com/836238
+  bool is_enum = (minimum == 1 &&
+                  static_cast<Sample>(bucket_count) == maximum - minimum + 2);
+  uint32_t checksum = static_cast<uint32_t>(bucket_count + 1);
+  checksum = Crc32(checksum, 0);
+  debug::Alias(&minimum);
+  debug::Alias(&maximum);
+  debug::Alias(&min);
+  debug::Alias(&max);
+  debug::Alias(&bucket_count);
+  debug::Alias(&checksum);
+  debug::Alias(&is_enum);
+
   for (size_t i = 1; i < bucket_count; ++i) {
     double linear_range =
         (min * (bucket_count - 1 - i) + max * (i - 1)) / (bucket_count - 2);
-    ranges->set_range(i, static_cast<Sample>(linear_range + 0.5));
+    uint32_t range = static_cast<Sample>(linear_range + 0.5);
+    if (is_enum)
+      CHECK_EQ(static_cast<uint32_t>(i), range);
+    ranges->set_range(i, range);
+    checksum = Crc32(checksum, range);
   }
   ranges->set_range(ranges->bucket_count(), HistogramBase::kSampleType_MAX);
   ranges->ResetChecksum();
+  checksum = Crc32(checksum, HistogramBase::kSampleType_MAX);
+  CHECK_EQ(checksum, ranges->checksum());
 }
 
 // static