mash: Store chrome --mash crash key metadata in shared memory

chrome/app/mash/mash_crash_keys.cc

+// Copyright 2017 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 "chrome/app/mash/mash_crash_keys.h"
+
+#include <fcntl.h>  // For O_ constants.
+#include <stdlib.h>
+#include <sys/mman.h>  // For shm_mem().
+#include <unistd.h>
+
+#include <string>
+#include <vector>
+
+#include "base/debug/crash_logging.h"
+#include "base/logging.h"
+#include "base/strings/string_piece.h"
+#include "base/strings/stringprintf.h"
+#include "breakpad/src/common/simple_string_dictionary.h"
+#include "components/crash/core/common/crash_keys.h"
+
+using google_breakpad::SimpleStringDictionary;
+
+namespace mash_crash_keys {
+namespace {
+
+// The size of the shared memory buffer for crash keys.
+const size_t kSharedMemorySize = sizeof(SimpleStringDictionary);
+
+// The shared memory name, including a trailing pid. The name is shared with
+// crash_reporter, see src/platform2/crash-reporter/user_collector.cc.
+const char kSharedMemoryNameFormat[] = "/chrome_crash_keys_%d";
+
+// File descriptor for the shared memory buffer containing the crash key
+// dictionary.
+int g_shared_memory_fd = -1;
+
+SimpleStringDictionary* g_crash_key_dictionary = nullptr;
+
+void SetCrashKey(const base::StringPiece& key, const base::StringPiece& value) {
+  g_crash_key_dictionary->SetKeyValue(key.data(), value.data());

[hashimoto, 2017/03/02 07:42:22]

base/strings/string_piece.h says StrinbPiece::data() shouldn't be used when a
NUL terminated string is expected.
https://cs.chromium.org/chromium/src/base/strings/string_piece.h?q=file:base/...

+}
+
+void ClearCrashKey(const base::StringPiece& key) {
+  g_crash_key_dictionary->RemoveKey(key.data());

[hashimoto, 2017/03/02 07:42:22]

ditto.

+}
+
+void CreateSharedMemoryDictionary() {
+  CHECK(!g_crash_key_dictionary);
+
+  // Create a shared memory buffer with a well-known name. Chrome unlinks
+  // the shared memory buffer below for normal exit. The OS crash_reporter
+  // unlinks the buffer for crashes.
+  const std::string shared_memory_name =
+      base::StringPrintf(kSharedMemoryNameFormat, getpid());
+  const int oflag = O_CREAT | O_RDWR;

[vapier, 2017/03/11 06:14:59]

i don't think this exec's, so should use O_CLOEXEC everywhere unless you need it

+  // Make user-only read-write (not group or world). crash_reporter runs as root
+  // and can read the buffer regardless.
+  const mode_t mode = S_IRUSR | S_IWUSR;

[vapier, 2017/03/11 06:14:59]

S_xxx constants aren't readable.  just use an octal constant like 0600.

+  g_shared_memory_fd = shm_open(shared_memory_name.c_str(), oflag, mode);

[hashimoto, 2017/03/02 07:42:22]

Can't we just use utilities in base/memory/shared_memory_helper.h and
base/memory/shared_memory.h?

+  PCHECK(g_shared_memory_fd != -1);
+
+  // Set the size of the buffer. The bytes are automatically initialized to 0.
+  int result = ftruncate(g_shared_memory_fd, kSharedMemorySize);

[hashimoto, 2017/03/02 07:42:22]

Please use HANDLE_EINTR.
ftruncate may return EINTR.

+  PCHECK(result != -1);
+
+  // Map the buffer as read-write memory.
+  void* buffer = mmap(nullptr, kSharedMemorySize, PROT_READ | PROT_WRITE,
+                      MAP_SHARED, g_shared_memory_fd, 0 /* offset */);
+  PCHECK(buffer != MAP_FAILED);
+
+  // Memory filled with 0 is a valid empty SimpleStringDictionary.

[hashimoto, 2017/03/02 07:42:22]

Please use placement new, so that you don't have to have this assumption.

g_crash_key_dictionary = new (buffer) SimpleStringDictionary();

+  g_crash_key_dictionary = reinterpret_cast<SimpleStringDictionary*>(buffer);
+  DCHECK_EQ(0u, g_crash_key_dictionary->GetCount());
+}
+
+void RegisterCrashKeys() {

[hashimoto, 2017/03/02 07:42:22]

If you want to allow processes which cannot depend on chrome code to register
these crash keys, please move the corresponding part of
RegisterChromeCrashKeys() in chrome/common/crash_keys.cc to somewhere those
processes can depend on.

+  // Register keys used by non-browser processes launched by the service manager
+  // (e.g. the GPU service). See chrome/common/crash_keys.cc.
+  std::vector<base::debug::CrashKey> keys = {
+      {"url-chunk", crash_keys::kLargeSize},

[hashimoto, 2017/03/02 07:42:22]

Please use the constants defined in the appropriate header.

+      {"total-discardable-memory-allocated", crash_keys::kSmallSize},
+      {"discardable-memory-free", crash_keys::kSmallSize},
+  };
+  crash_keys::GetCrashKeysForCommandLineSwitches(&keys);
+  base::debug::InitCrashKeys(&keys.at(0), keys.size(),
+                             crash_keys::kChunkMaxLength);
+}
+
+}  // namespace
+
+void Initialize() {
+  CHECK(!g_crash_key_dictionary);
+  CreateSharedMemoryDictionary();
+  RegisterCrashKeys();
+  base::debug::SetCrashKeyReportingFunctions(&SetCrashKey, &ClearCrashKey);
+}
+
+void Shutdown() {
+  CHECK(g_crash_key_dictionary);
+  int result = munmap(g_crash_key_dictionary, kSharedMemorySize);
+  PCHECK(result != -1);
+  g_crash_key_dictionary = nullptr;
+
+  result = close(g_shared_memory_fd);
+  PCHECK(result != -1);
+  g_shared_memory_fd = -1;
+
+  const std::string shared_memory_name =
+      base::StringPrintf(kSharedMemoryNameFormat, getpid());
+  result = shm_unlink(shared_memory_name.c_str());
+  PCHECK(result != -1);
+}
+
+int GetSharedMemoryFdForTesting() {
+  return g_shared_memory_fd;
+}
+
+size_t GetCrashKeyCountForTesting() {
+  return g_crash_key_dictionary->GetCount();
+}
+
+}  // namespace mash_crash_keys