Rationalize and fix chromium android linker histogram recording.

base/android/library_loader/library_loader_hooks.cc

 // Copyright 2014 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/android/library_loader/library_loader_hooks.h"
 
 #include "base/android/command_line_android.h"
 #include "base/android/jni_string.h"
 #include "base/at_exit.h"
 #include "base/metrics/histogram.h"
 #include "jni/LibraryLoader_jni.h"
 
 namespace base {
 namespace android {
 
 namespace {
 
 base::AtExitManager* g_at_exit_manager = NULL;
 const char* g_library_version_number = "";
 LibraryLoadedHook* g_registration_callback = NULL;
 
+enum RendererHistogramCode {
+  // Renderer load at fixed address success, fail, or not attempted.
+  // Renderers do not attempt to load at at fixed address if on a
+  // low-memory device on which browser load at fixed address has already
+  // failed.
+  LFA_SUCCESS = 0,
+  LFA_BACKOFF_USED = 1,
+  LFA_NOT_ATTEMPTED = 2,
+
+  // End sentinel, also used as nothing-pending indicator.
+  MAX_RENDERER_HISTOGRAM_CODE = 3,
+  NO_PENDING_HISTOGRAM_CODE = MAX_RENDERER_HISTOGRAM_CODE
+};
+
+enum BrowserHistogramCode {
+  // Non-low-memory random address browser loads.
+  NORMAL_LRA_SUCCESS = 0,
+
+  // Low-memory browser loads at fixed address, success or fail.
+  LOW_MEMORY_LFA_SUCCESS = 1,
+  LOW_MEMORY_LFA_BACKOFF_USED = 2,
+
+  MAX_BROWSER_HISTOGRAM_CODE = 3,
+};
+
+RendererHistogramCode g_renderer_histogram_code = NO_PENDING_HISTOGRAM_CODE;
+
 } // namespace
 
+static void RegisterChromiumAndroidLinkerRendererHistogram(
+    JNIEnv* env,
+    jclass clazz,
+    jboolean requested_shared_relro,
+    jboolean load_at_fixed_address_failed) {
+  // Note a pending histogram value for later recording.
+  if (requested_shared_relro) {
+    g_renderer_histogram_code = load_at_fixed_address_failed
+                                ? LFA_BACKOFF_USED : LFA_SUCCESS;
+  } else {
+    g_renderer_histogram_code = LFA_NOT_ATTEMPTED;
+  }
+}
+
+void RecordChromiumAndroidLinkerRendererHistogram() {
+  if (g_renderer_histogram_code == NO_PENDING_HISTOGRAM_CODE)
+    return;
+  // Record and release the pending histogram value.
+  UMA_HISTOGRAM_ENUMERATION("ChromiumAndroidLinker.RendererStates",
+                            g_renderer_histogram_code,
+                            MAX_RENDERER_HISTOGRAM_CODE);
+  g_renderer_histogram_code = NO_PENDING_HISTOGRAM_CODE;
+}

[Ilya Sherman, 2014/10/02 20:53:57]

Why do you need the pending histogram value, rather than just recording this
histogram when the value is set?

[simonb (inactive), 2014/10/03 11:51:42]

The value appears when loading libchrome.so, and this is too early for
histograms to work.  The solution is to save it here as 'pending', and push it
to histograms later and once library code is running.

+
+static void RecordChromiumAndroidLinkerBrowserHistogram(
+    JNIEnv* env,
+    jclass clazz,
+    jboolean is_using_browser_shared_relros,
+    jboolean load_at_fixed_address_failed) {
+  // For low-memory devices, record whether or not we successfully loaded the
+  // browser at a fixed address. Otherwise just record a normal invocation.
+  BrowserHistogramCode histogram_code;
+  if (is_using_browser_shared_relros) {
+    histogram_code = load_at_fixed_address_failed
+                     ? LOW_MEMORY_LFA_BACKOFF_USED : LOW_MEMORY_LFA_SUCCESS;
+  } else {
+    histogram_code = NORMAL_LRA_SUCCESS;
+  }
+  UMA_HISTOGRAM_ENUMERATION("ChromiumAndroidLinker.BrowserStates",
+                            histogram_code,
+                            MAX_BROWSER_HISTOGRAM_CODE);
+}
+
 void SetLibraryLoadedHook(LibraryLoadedHook* func) {
   g_registration_callback = func;
 }
 
 static void InitCommandLine(JNIEnv* env, jclass clazz,
                             jobjectArray init_command_line) {
   InitNativeCommandLineFromJavaArray(env, init_command_line);
 }
 
 static jboolean LibraryLoaded(JNIEnv* env, jclass clazz) {
-  if(g_registration_callback == NULL) {
+  if (g_registration_callback == NULL) {
     return true;
   }
   return g_registration_callback(env, clazz);
 }
 
-static void RecordChromiumAndroidLinkerHistogram(
-    JNIEnv* env,
-    jclass clazz,
-    jboolean loaded_at_fixed_address_failed,
-    jboolean is_low_memory_device) {
-  UMA_HISTOGRAM_BOOLEAN("ChromiumAndroidLinker.LoadedAtFixedAddressFailed",
-                        loaded_at_fixed_address_failed);
-  UMA_HISTOGRAM_BOOLEAN("ChromiumAndroidLinker.IsLowMemoryDevice",
-                        is_low_memory_device);

[Ilya Sherman, 2014/10/02 20:53:57]

Please mark the corresponding histograms as <obsolete>

[simonb (inactive), 2014/10/03 11:51:42]

Done.

-}
-
 void LibraryLoaderExitHook() {
   if (g_at_exit_manager) {
     delete g_at_exit_manager;
     g_at_exit_manager = NULL;
   }
 }
 
 bool RegisterLibraryLoaderEntryHook(JNIEnv* env) {
   // We need the AtExitManager to be created at the very beginning.
   g_at_exit_manager = new base::AtExitManager();
 
   return RegisterNativesImpl(env);
 }
 
 void SetVersionNumber(const char* version_number) {
   g_library_version_number = strdup(version_number);
 }
 
 jstring GetVersionNumber(JNIEnv* env, jclass clazz) {
   return ConvertUTF8ToJavaString(env, g_library_version_number).Release();
 }
 
 static void RecordNativeLibraryHack(JNIEnv*, jclass, jboolean usedHack) {
   UMA_HISTOGRAM_BOOLEAN("LibraryLoader.NativeLibraryHack", usedHack);
 }
 
 }  // namespace android
 }  // namespace base