Sync with upstream repo.

Changes include:
* CPU check has been broken up into a number of small libraries
* BoringSSL option has been removed
* Better abseil integration

silkscreen.h

@@ -0,0 +1,63 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <map>
+#include <vector>
+#include "absl/status/status.h"
+
+#ifndef THIRD_PARTY_CPU_CHECK_SILKSCREEN_H_
+#define THIRD_PARTY_CPU_CHECK_SILKSCREEN_H_
+
+namespace cpu_check {
+// Rudimentary coherence/uncore tester.
+// Randomly assigns each slot of a seemingly shared buffer to a single tid,
+// creating only "false sharing".
+// Thus each slot, regardless of alignment, must obey program order unless the
+// machine is broken.
+// To be toughened, e.g.:
+//   Widen the slots a bit
+//   Control the sharing more tightly, e.g. each cache line split between 2 tids
+//   Maybe checksum the indices to distinguish core-local compute errors from
+//   coherence errors, but that's perhaps easier said than done effectively.
+// As it stands, it may be particularly hard to localize failures. Though that's
+// always going to be a bit hard, which is the point. One technique might be
+// to leave this alone and to run on subsets of cores and sockets.
+class Silkscreen {
+ public:
+  static constexpr size_t kSize = 1000 * 1000;  // Size of buffer
+
+  Silkscreen(const std::vector<int>& tid_list);
+  ~Silkscreen() { free(buffer_address_); }
+
+  // Writes value derived from 'round' into all slots owned by 'tid'.
+  // Returns non-OK Status with JSON-formatted message upon error.
+  absl::Status WriteMySlots(int tid, uint64_t round);
+
+  // Checks all slots owned by 'tid' for value appropriate to 'round'.
+  // Returns non-OK Status with JSON-formatted message upon error.
+  absl::Status CheckMySlots(int tid, uint64_t round) const;
+
+ private:
+  int owner(size_t k) const { return owner_[k]; }
+  size_t size() const { return owner_.size(); }
+  int slot_count(int owner) const { return slot_count_.at(owner); }
+  const char* data(size_t k) const { return buffer_address_ + k; }
+  char* data(size_t k) { return buffer_address_ + k; }
+
+  std::vector<uint16_t> owner_;    // const after initialization
+  std::map<int, int> slot_count_;  // const after initialization
+  char* const buffer_address_;
+};
+}  // namespace cpu_check
+#endif  // THIRD_PARTY_CPU_CHECK_SILKSCREEN_H_