diff --git a/include/nativebridge/native_bridge.h b/include/nativebridge/native_bridge.h
index 16939f1..ac254e9 100644
--- a/include/nativebridge/native_bridge.h
+++ b/include/nativebridge/native_bridge.h
@@ -19,18 +19,29 @@
 
 #include "jni.h"
 #include <stdint.h>
+#include <sys/types.h>
 
 namespace android {
 
 struct NativeBridgeRuntimeCallbacks;
+struct NativeBridgeRuntimeValues;
 
 // Open the native bridge, if any. Should be called by Runtime::Init(). A null library filename
 // signals that we do not want to load a native bridge.
 bool LoadNativeBridge(const char* native_bridge_library_filename,
                       const NativeBridgeRuntimeCallbacks* runtime_callbacks);
 
-// Initialize the native bridge, if any. Should be called by Runtime::DidForkFromZygote.
-bool InitializeNativeBridge();
+// Quick check whether a native bridge will be needed. This is based off of the instruction set
+// of the process.
+bool NeedsNativeBridge(const char* instruction_set);
+
+// Do the early initialization part of the native bridge, if necessary. This should be done under
+// high privileges.
+void PreInitializeNativeBridge(const char* app_data_dir, const char* instruction_set);
+
+// Initialize the native bridge, if any. Should be called by Runtime::DidForkFromZygote. The JNIEnv*
+// will be used to modify the app environment for the bridge.
+bool InitializeNativeBridge(JNIEnv* env, const char* instruction_set);
 
 // Unload the native bridge, if any. Should be called by Runtime::DidForkFromZygote.
 void UnloadNativeBridge();
@@ -65,6 +76,9 @@
 
 // Native bridge interfaces to runtime.
 struct NativeBridgeCallbacks {
+  // Version number of the interface.
+  uint32_t version;
+
   // Initialize native bridge. Native bridge's internal implementation must ensure MT safety and
   // that the native bridge is initialized only once. Thus it is OK to call this interface for an
   // already initialized native bridge.
@@ -73,7 +87,8 @@
   //   runtime_cbs [IN] the pointer to NativeBridgeRuntimeCallbacks.
   // Returns:
   //   true iff initialization was successful.
-  bool (*initialize)(const NativeBridgeRuntimeCallbacks* runtime_cbs);
+  bool (*initialize)(const NativeBridgeRuntimeCallbacks* runtime_cbs, const char* private_dir,
+                     const char* instruction_set);
 
   // Load a shared library that is supported by the native bridge.
   //
@@ -102,6 +117,16 @@
   // Returns:
   //   TRUE if library is supported by native bridge, FALSE otherwise
   bool (*isSupported)(const char* libpath);
+
+  // Provide environment values required by the app running with native bridge according to the
+  // instruction set.
+  //
+  // Parameters:
+  //    instruction_set [IN] the instruction set of the app
+  // Returns:
+  //    NULL if not supported by native bridge.
+  //    Otherwise, return all environment values to be set after fork.
+  const struct NativeBridgeRuntimeValues* (*getAppEnv)(const char* instruction_set);
 };
 
 // Runtime interfaces to native bridge.
diff --git a/libnativebridge/Android.mk b/libnativebridge/Android.mk
index 3009bb9..6c2e43e 100644
--- a/libnativebridge/Android.mk
+++ b/libnativebridge/Android.mk
@@ -13,7 +13,7 @@
 LOCAL_SHARED_LIBRARIES := liblog
 LOCAL_CLANG := true
 LOCAL_CPP_EXTENSION := .cc
-LOCAL_CFLAGS := -Werror
+LOCAL_CFLAGS := -Werror -Wall
 LOCAL_CPPFLAGS := -std=gnu++11 -fvisibility=protected
 LOCAL_LDFLAGS := -ldl
 LOCAL_MULTILIB := both
@@ -30,7 +30,7 @@
 LOCAL_SHARED_LIBRARIES := liblog
 LOCAL_CLANG := true
 LOCAL_CPP_EXTENSION := .cc
-LOCAL_CFLAGS := -Werror
+LOCAL_CFLAGS := -Werror -Wall
 LOCAL_CPPFLAGS := -std=gnu++11 -fvisibility=protected
 LOCAL_LDFLAGS := -ldl
 LOCAL_MULTILIB := both
diff --git a/libnativebridge/native_bridge.cc b/libnativebridge/native_bridge.cc
index 6602d3f..d460f6f 100644
--- a/libnativebridge/native_bridge.cc
+++ b/libnativebridge/native_bridge.cc
@@ -16,13 +16,27 @@
 
 #include "nativebridge/native_bridge.h"
 
+#include <cstring>
 #include <cutils/log.h>
 #include <dlfcn.h>
+#include <errno.h>
+#include <fcntl.h>
 #include <stdio.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
 
 
 namespace android {
 
+// Environment values required by the apps running with native bridge.
+struct NativeBridgeRuntimeValues {
+    const char* os_arch;
+    const char* cpu_abi;
+    const char* cpu_abi2;
+    const char* *supported_abis;
+    int32_t abi_count;
+};
+
 // The symbol name exposed by native-bridge with the type of NativeBridgeCallbacks.
 static constexpr const char* kNativeBridgeInterfaceSymbol = "NativeBridgeItf";
 
@@ -68,6 +82,11 @@
 // Callbacks provided by the environment to the bridge. Passed to LoadNativeBridge.
 static const NativeBridgeRuntimeCallbacks* runtime_callbacks = nullptr;
 
+// The app's data directory.
+static char* app_data_dir = nullptr;
+
+static constexpr uint32_t kNativeBridgeCallbackVersion = 1;
+
 // Characters allowed in a native bridge filename. The first character must
 // be in [a-zA-Z] (expected 'l' for "libx"). The rest must be in [a-zA-Z0-9._-].
 static bool CharacterAllowed(char c, bool first) {
@@ -109,6 +128,10 @@
   }
 }
 
+static bool VersionCheck(NativeBridgeCallbacks* cb) {
+  return cb != nullptr && cb->version == kNativeBridgeCallbackVersion;
+}
+
 bool LoadNativeBridge(const char* nb_library_filename,
                       const NativeBridgeRuntimeCallbacks* runtime_cbs) {
   // We expect only one place that calls LoadNativeBridge: Runtime::Init. At that point we are not
@@ -116,8 +139,10 @@
 
   if (state != NativeBridgeState::kNotSetup) {
     // Setup has been called before. Ignore this call.
-    ALOGW("Called LoadNativeBridge for an already set up native bridge. State is %s.",
-          GetNativeBridgeStateString(state));
+    if (nb_library_filename != nullptr) {  // Avoids some log-spam for dalvikvm.
+      ALOGW("Called LoadNativeBridge for an already set up native bridge. State is %s.",
+            GetNativeBridgeStateString(state));
+    }
     // Note: counts as an error, even though the bridge may be functional.
     had_error = true;
     return false;
@@ -137,8 +162,14 @@
         callbacks = reinterpret_cast<NativeBridgeCallbacks*>(dlsym(handle,
                                                                    kNativeBridgeInterfaceSymbol));
         if (callbacks != nullptr) {
-          // Store the handle for later.
-          native_bridge_handle = handle;
+          if (VersionCheck(callbacks)) {
+            // Store the handle for later.
+            native_bridge_handle = handle;
+          } else {
+            callbacks = nullptr;
+            dlclose(handle);
+            ALOGW("Unsupported native bridge interface.");
+          }
         } else {
           dlclose(handle);
         }
@@ -158,13 +189,217 @@
   }
 }
 
-bool InitializeNativeBridge() {
+#if defined(__arm__)
+static const char* kRuntimeISA = "arm";
+#elif defined(__aarch64__)
+static const char* kRuntimeISA = "arm64";
+#elif defined(__mips__)
+static const char* kRuntimeISA = "mips";
+#elif defined(__i386__)
+static const char* kRuntimeISA = "x86";
+#elif defined(__x86_64__)
+static const char* kRuntimeISA = "x86_64";
+#else
+static const char* kRuntimeISA = "unknown";
+#endif
+
+
+bool NeedsNativeBridge(const char* instruction_set) {
+  if (instruction_set == nullptr) {
+    ALOGE("Null instruction set in NeedsNativeBridge.");
+    return false;
+  }
+  return strncmp(instruction_set, kRuntimeISA, strlen(kRuntimeISA) + 1) != 0;
+}
+
+#ifdef __APPLE__
+template<typename T> void UNUSED(const T&) {}
+#endif
+
+void PreInitializeNativeBridge(const char* app_data_dir_in, const char* instruction_set) {
+  if (app_data_dir_in == nullptr) {
+    return;
+  }
+
+  const size_t len = strlen(app_data_dir_in);
+  // Make a copy for us.
+  app_data_dir = new char[len];
+  strncpy(app_data_dir, app_data_dir_in, len);
+
+#ifndef __APPLE__
+  if (instruction_set == nullptr) {
+    return;
+  }
+  size_t isa_len = strlen(instruction_set);
+  if (isa_len > 10) {
+    // 10 is a loose upper bound on the currently known instruction sets (a tight bound is 7 for
+    // x86_64 [including the trailing \0]). This is so we don't have to change here if there will
+    // be another instruction set in the future.
+    ALOGW("Instruction set %s is malformed, must be less than or equal to 10 characters.",
+          instruction_set);
+    return;
+  }
+
+  // Bind-mount /system/lib{,64}/<isa>/cpuinfo to /proc/cpuinfo. If the file does not exist, the
+  // mount command will fail, so we safe the extra file existence check...
+  char cpuinfo_path[1024];
+
+#ifdef HAVE_ANDROID_OS
+  snprintf(cpuinfo_path, sizeof(cpuinfo_path), "/system/lib"
+#ifdef __LP64__
+      "64"
+#endif  // __LP64__
+      "/%s/cpuinfo", instruction_set);
+#else   // !HAVE_ANDROID_OS
+  // To be able to test on the host, we hardwire a relative path.
+  snprintf(cpuinfo_path, sizeof(cpuinfo_path), "./cpuinfo");
+#endif
+
+  // Bind-mount.
+  if (TEMP_FAILURE_RETRY(mount(cpuinfo_path,        // Source.
+                               "/proc/cpuinfo",     // Target.
+                               nullptr,             // FS type.
+                               MS_BIND,             // Mount flags: bind mount.
+                               nullptr)) == -1) {   // "Data."
+    ALOGW("Failed to bind-mount %s as /proc/cpuinfo: %s", cpuinfo_path, strerror(errno));
+  }
+#else
+  UNUSED(instruction_set);
+  ALOGW("Mac OS does not support bind-mounting. Host simulation of native bridge impossible.");
+#endif
+}
+
+static void SetCpuAbi(JNIEnv* env, jclass build_class, const char* field, const char* value) {
+  if (value != nullptr) {
+    jfieldID field_id = env->GetStaticFieldID(build_class, field, "Ljava/lang/String;");
+    if (field_id == nullptr) {
+      env->ExceptionClear();
+      ALOGW("Could not find %s field.", field);
+      return;
+    }
+
+    jstring str = env->NewStringUTF(value);
+    if (str == nullptr) {
+      env->ExceptionClear();
+      ALOGW("Could not create string %s.", value);
+      return;
+    }
+
+    env->SetStaticObjectField(build_class, field_id, str);
+  }
+}
+
+static void SetSupportedAbis(JNIEnv* env, jclass build_class, const char* field,
+                             const char* *values, int32_t value_count) {
+  if (value_count < 0) {
+    return;
+  }
+  if (values == nullptr && value_count > 0) {
+    ALOGW("More than zero values expected: %d.", value_count);
+    return;
+  }
+
+  jfieldID field_id = env->GetStaticFieldID(build_class, field, "[Ljava/lang/String;");
+  if (field_id != nullptr) {
+    // Create the array.
+    jobjectArray array = env->NewObjectArray(value_count, env->FindClass("java/lang/String"),
+                                             nullptr);
+    if (array == nullptr) {
+      env->ExceptionClear();
+      ALOGW("Could not create array.");
+      return;
+    }
+
+    // Fill the array.
+    for (int32_t i = 0; i < value_count; i++) {
+      jstring str = env->NewStringUTF(values[i]);
+      if (str == nullptr) {
+        env->ExceptionClear();
+        ALOGW("Could not create string %s.", values[i]);
+        return;
+      }
+
+      env->SetObjectArrayElement(array, i, str);
+    }
+
+    env->SetStaticObjectField(build_class, field_id, array);
+  } else {
+    env->ExceptionClear();
+    ALOGW("Could not find %s field.", field);
+  }
+}
+
+// Set up the environment for the bridged app.
+static void SetupEnvironment(NativeBridgeCallbacks* callbacks, JNIEnv* env, const char* isa) {
+  // Need a JNIEnv* to do anything.
+  if (env == nullptr) {
+    ALOGW("No JNIEnv* to set up app environment.");
+    return;
+  }
+
+  // Query the bridge for environment values.
+  const struct NativeBridgeRuntimeValues* env_values = callbacks->getAppEnv(isa);
+  if (env_values == nullptr) {
+    return;
+  }
+
+  // Keep the JNIEnv clean.
+  jint success = env->PushLocalFrame(16);  // That should be small and large enough.
+  if (success < 0) {
+    // Out of memory, really borked.
+    ALOGW("Out of memory while setting up app environment.");
+    env->ExceptionClear();
+    return;
+  }
+
+  // Reset CPU_ABI & CPU_ABI2 to values required by the apps running with native bridge.
+  if (env_values->cpu_abi != nullptr || env_values->cpu_abi2 != nullptr ||
+      env_values->abi_count >= 0) {
+    jclass bclass_id = env->FindClass("android/os/Build");
+    if (bclass_id != nullptr) {
+      SetCpuAbi(env, bclass_id, "CPU_ABI", env_values->cpu_abi);
+      SetCpuAbi(env, bclass_id, "CPU_ABI2", env_values->cpu_abi2);
+
+      SetSupportedAbis(env, bclass_id, "SUPPORTED_ABIS", env_values->supported_abis,
+                       env_values->abi_count);
+    } else {
+      // For example in a host test environment.
+      env->ExceptionClear();
+      ALOGW("Could not find Build class.");
+    }
+  }
+
+  if (env_values->os_arch != nullptr) {
+    jclass sclass_id = env->FindClass("java/lang/System");
+    if (sclass_id != nullptr) {
+      jmethodID set_prop_id = env->GetStaticMethodID(sclass_id, "setProperty",
+          "(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;");
+      if (set_prop_id != nullptr) {
+        // Reset os.arch to the value reqired by the apps running with native bridge.
+        env->CallStaticObjectMethod(sclass_id, set_prop_id, env->NewStringUTF("os.arch"),
+            env->NewStringUTF(env_values->os_arch));
+      } else {
+        env->ExceptionClear();
+        ALOGW("Could not find setProperty method.");
+      }
+    } else {
+      env->ExceptionClear();
+      ALOGW("Could not find System class.");
+    }
+  }
+
+  // Make it pristine again.
+  env->PopLocalFrame(nullptr);
+}
+
+bool InitializeNativeBridge(JNIEnv* env, const char* instruction_set) {
   // We expect only one place that calls InitializeNativeBridge: Runtime::DidForkFromZygote. At that
   // point we are not multi-threaded, so we do not need locking here.
 
   if (state == NativeBridgeState::kOpened) {
     // Try to initialize.
-    if (callbacks->initialize(runtime_callbacks)) {
+    if (callbacks->initialize(runtime_callbacks, app_data_dir, instruction_set)) {
+      SetupEnvironment(callbacks, env, instruction_set);
       state = NativeBridgeState::kInitialized;
     } else {
       // Unload the library.
diff --git a/libnativebridge/tests/Android.mk b/libnativebridge/tests/Android.mk
index 457b163..9c7e1b8 100644
--- a/libnativebridge/tests/Android.mk
+++ b/libnativebridge/tests/Android.mk
@@ -5,6 +5,8 @@
 # Build the unit tests.
 test_src_files := \
     InvalidCharsNativeBridge_test.cpp \
+    NeedsNativeBridge_test.cpp \
+    PreInitializeNativeBridge_test.cpp \
     ReSetupNativeBridge_test.cpp \
     UnavailableNativeBridge_test.cpp \
     ValidNameNativeBridge_test.cpp
diff --git a/libnativebridge/tests/NeedsNativeBridge_test.cpp b/libnativebridge/tests/NeedsNativeBridge_test.cpp
new file mode 100644
index 0000000..e1c0876
--- /dev/null
+++ b/libnativebridge/tests/NeedsNativeBridge_test.cpp
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * 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 "NativeBridgeTest.h"
+
+namespace android {
+
+static const char* kISAs[] = { "arm", "arm64", "mips", "x86", "x86_64", "random", "64arm", "64_x86",
+                               "64_x86_64", "", "reallylongstringabcd", nullptr };
+
+#if defined(__arm__)
+static const char* kRuntimeISA = "arm";
+#elif defined(__aarch64__)
+static const char* kRuntimeISA = "arm64";
+#elif defined(__mips__)
+static const char* kRuntimeISA = "mips";
+#elif defined(__i386__)
+static const char* kRuntimeISA = "x86";
+#elif defined(__x86_64__)
+static const char* kRuntimeISA = "x86_64";
+#else
+static const char* kRuntimeISA = "unknown";
+#endif
+
+TEST_F(NativeBridgeTest, NeedsNativeBridge) {
+    EXPECT_EQ(false, NeedsNativeBridge(kRuntimeISA));
+
+    const size_t kISACount = sizeof(kISAs)/sizeof(kISAs[0]);
+    for (size_t i = 0; i < kISACount; i++) {
+        EXPECT_EQ(kISAs[i] == nullptr ? false : strcmp(kISAs[i], kRuntimeISA) != 0,
+                  NeedsNativeBridge(kISAs[i]));
+    }
+}
+
+}  // namespace android
diff --git a/libnativebridge/tests/PreInitializeNativeBridge_test.cpp b/libnativebridge/tests/PreInitializeNativeBridge_test.cpp
new file mode 100644
index 0000000..9b487d7
--- /dev/null
+++ b/libnativebridge/tests/PreInitializeNativeBridge_test.cpp
@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * 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 "NativeBridgeTest.h"
+
+#include <cstdio>
+#include <cstring>
+#include <cutils/log.h>
+#include <dlfcn.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+
+namespace android {
+
+static constexpr const char* kTestData = "PreInitializeNativeBridge test.";
+
+TEST_F(NativeBridgeTest, PreInitializeNativeBridge) {
+#ifndef __APPLE_         // Mac OS does not support bind-mount.
+#ifndef HAVE_ANDROID_OS  // Cannot write into the hard-wired location.
+    // Try to create our mount namespace.
+    if (unshare(CLONE_NEWNS) != -1) {
+        // Create a dummy file.
+        FILE* cpuinfo = fopen("./cpuinfo", "w");
+        ASSERT_NE(nullptr, cpuinfo) << strerror(errno);
+        fprintf(cpuinfo, kTestData);
+        fclose(cpuinfo);
+
+        // Call the setup.
+        PreInitializeNativeBridge("does not matter 1", "short 2");
+
+        // Read /proc/cpuinfo
+        FILE* proc_cpuinfo = fopen("/proc/cpuinfo", "r");
+        ASSERT_NE(nullptr, proc_cpuinfo) << strerror(errno);
+        char buf[1024];
+        EXPECT_NE(nullptr, fgets(buf, sizeof(buf), proc_cpuinfo)) << "Error reading.";
+        fclose(proc_cpuinfo);
+
+        EXPECT_EQ(0, strcmp(buf, kTestData));
+
+        // Delete the file.
+        ASSERT_EQ(0, unlink("./cpuinfo")) << "Error unlinking temporary file.";
+        // Ending the test will tear down the mount namespace.
+    } else {
+        GTEST_LOG_(WARNING) << "Could not create mount namespace. Are you running this as root?";
+    }
+#endif
+#endif
+}
+
+}  // namespace android
diff --git a/libnativebridge/tests/UnavailableNativeBridge_test.cpp b/libnativebridge/tests/UnavailableNativeBridge_test.cpp
index ec96c32..ad374a5 100644
--- a/libnativebridge/tests/UnavailableNativeBridge_test.cpp
+++ b/libnativebridge/tests/UnavailableNativeBridge_test.cpp
@@ -21,7 +21,7 @@
 TEST_F(NativeBridgeTest, NoNativeBridge) {
     EXPECT_EQ(false, NativeBridgeAvailable());
     // Try to initialize. This should fail as we are not set up.
-    EXPECT_EQ(false, InitializeNativeBridge());
+    EXPECT_EQ(false, InitializeNativeBridge(nullptr, nullptr));
     EXPECT_EQ(true, NativeBridgeError());
     EXPECT_EQ(false, NativeBridgeAvailable());
 }