Android: Add chrome-specific dynamic linker.

base/android/linker/crazy_linker_jni.cpp

+// Copyright 2013 The Chromium Authors. All rights reserved.

[bulach, 2013/09/09 11:43:18]

nit: this file should be .cc rather than ".cpp"..

also, "crazy" sounds great :) but it's not too descriptive (or is it??)

how about just "custom_linker" or "shared_sections_linker"?

[digit1, 2013/09/10 09:23:30]

I've renamed it to crazy_linker_jni.cc for now.

I'm open to different names, but we have plans to experiment with other features
in the future so "shared_sections_linker" sounds a bit too tied to an
implementation detail. libcustom_linker.so doesn't have the same "cachet" to me.
Possible alternatives:

  liblinker.so
  libbase_linker.so
  libcontent_linker.so
  libchromium_linker.so
  libchrome_linker.so

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This is the Android-specific Chrome linker, a tiny shared library
+// implementing a custom dynamic linker that can be used to load the
+// real Chrome libraries (e.g. libchromeview.so).
+
+// The main point of this linker is to be able to share the RELRO
+// section of libchromeview.so between the browser and renderer
+// process. This saves about 1.3 MB of private RAM per renderer process.
+
+#include <stdlib.h>
+
+#include <android/log.h>
+#include <jni.h>
+#include <crazy_linker.h>
+
+// Set this to 1 to enable debug traces to the Android log.

[bulach, 2013/09/09 11:43:18]

add some comments saying it can't use LOG(..) because it happens before the
LOG(...) module is even initialized..

[digit1, 2013/09/10 09:23:30]

Done.

+#define DEBUG 0
+
+#if DEBUG
+#define LOG_INFO(...) \
+  __android_log_print(ANDROID_LOG_INFO, "chrome_linker", __VA_ARGS__)
+#define LOG_ERROR(...)  \
+  __android_log_print(ANDROID_LOG_ERROR, "chrome_linker", __VA_ARGS__)
+#else
+#define LOG_INFO(...)  ((void)0)
+#define LOG_ERROR(...) ((void)0)
+#endif
+
+#define UNUSED  __attribute__((unused))
+
+namespace {
+
+// A simply scoped UTF String class that can be initialized from
+// a Java jstring handle.

[bulach, 2013/09/09 11:43:18]

hmm... would base::android::jni_string.h methods work?

std::string str(ConvertJavaStringToUTF8(env, jstr));

[digit1, 2013/09/10 09:23:30]

No, the goal is to avoid any code that's part of base/ or the C++ STL to avoid
bloating the linker itself. That could easily a ton of code which would itself
require more RAM pages to load and relocate. This source intentionally avoids
any other dependencies, hence the reimplementations here.

I'll clarify that in a comment here.

+class String {
+public:

[jar (doing other things), 2013/09/06 17:08:50]

Should this comply with Chromium style?  If so, indent public/private by one
space.

[digit1, 2013/09/10 09:23:30]

I've done that. By the way, using "git cl format" here generates plenty of lines
that are > 80 characters. Did the style guide changed recently?

[Nico, 2013/09/10 14:57:20]

No. That's probably a clang-format bug. Make sure you're using clang-format
head, and file a bug at http://llvm.org/bugs (component clang subcomponent
formatter) (or go/clang-format-bug)

+  String(JNIEnv* env, jstring str);
+
+  ~String() {
+    if (ptr_)
+      ::free(ptr_);
+  }
+
+  const char* c_str() const { return ptr_ ? ptr_ : ""; }
+  size_t size() const { return size_; }
+
+private:
+  char* ptr_;
+  size_t size_;
+};
+
+String::String(JNIEnv* env, jstring str) {
+  size_ = env->GetStringUTFLength(str);
+  ptr_ = reinterpret_cast<char*>(::malloc(size_ + 1));
+
+  // Note: the result contains Java "modified UTF-8" bytes.
+  // Good enough for the linker though.
+  const char* bytes = env->GetStringUTFChars(str, NULL);
+  ::memcpy(ptr_, bytes, size_);
+  ptr_[size_] = '\0';
+
+  env->ReleaseStringUTFChars(str, bytes);
+}
+
+// A scoped crazy_library_t that automatically closes the handle
+// on scope exit, unless Release() has been called.
+class ScopedLibrary {
+public:
+  ScopedLibrary() : lib_(NULL) {}
+
+  ~ScopedLibrary() {
+    if (lib_)
+      crazy_library_close(lib_);
+  }
+
+  crazy_library_t* Get() { return lib_; }
+
+  crazy_library_t** GetPtr() { return &lib_; }
+
+  crazy_library_t* Release() {
+    crazy_library_t* ret = lib_;
+    lib_ = NULL;
+    return ret;
+  }
+
+private:
+  crazy_library_t* lib_;
+};
+
+static const char* GetBaseNamePtr(const char* path) {

[Nico, 2013/09/08 21:24:57]

(do you need the static? this is already in an unnamed namespace)

[digit1, 2013/09/10 09:23:30]

Indeed, I've removed the static. Thanks.

+  const char* p = strchr(path, '/');
+  if (p)
+    return p + 1;
+  else

[jar (doing other things), 2013/09/06 17:08:50]

nit: no need for else.

[digit1, 2013/09/10 09:23:30]

Done.

+    return path;
+}
+
+static bool InitClassReference(JNIEnv* env,
+                               const char* class_name,
+                               jclass* clazz) {
+  *clazz = env->FindClass(class_name);
+  if (!*clazz) {
+    LOG_ERROR("Could not find class for %s", class_name);
+    return false;
+  }
+  return true;
+}
+
+static bool InitFieldId(JNIEnv* env,

[bulach, 2013/09/09 11:43:18]

it'd be simpler to just use @CalledByNative and the JNI machinery here..

[digit1, 2013/09/10 09:23:30]

No, we can't use the machinery, because it relies on helper functions in base/
that I don't need to use here (this bloats the linker to about 300 KB :-(, also
doesn't work well with the component build where you can't statically link base
into this library).

+                        jclass clazz,
+                        const char* field_name,
+                        const char* field_sig,
+                        jfieldID* field_id) {
+  *field_id = env->GetFieldID(clazz, field_name, field_sig);
+  if (!*field_id) {
+    LOG_ERROR("Could not find ID for field '%s'", field_name);
+    return false;
+  }
+  LOG_INFO(
+      "%s: Found ID %p for field '%s", __FUNCTION__, *field_id, field_name);
+  return true;
+}
+
+
+static JavaVM* s_java_vm;
+
+struct LibInfo_class {
+  jfieldID load_address_id;
+  jfieldID load_size_id;
+  jfieldID relro_start_id;
+  jfieldID relro_size_id;
+  jfieldID relro_fd_id;
+
+  // Initialize an instance.
+  bool Init(JNIEnv* env) {
+    jclass clazz;
+    if (!InitClassReference(env,
+                            "org/chromium/base/Linker$LibInfo",
+                            &clazz)) {
+      return false;
+    }
+
+    return InitFieldId(env, clazz, "mLoadAddress", "J", &load_address_id) &&
+           InitFieldId(env, clazz, "mLoadSize", "J", &load_size_id) &&
+           InitFieldId(env, clazz, "mRelroStart", "J", &relro_start_id) &&
+           InitFieldId(env, clazz, "mRelroSize", "J", &relro_size_id) &&
+           InitFieldId(env, clazz, "mRelroFd", "I", &relro_fd_id);
+  }
+
+  // Use this instance to convert a RelroInfo reference into
+  // a crazy_library_info_t.
+  void GetLibraryInfo(JNIEnv* env,
+                      jobject library_info_obj,
+                      crazy_library_info_t* info) {
+    info->load_address = static_cast<size_t>(
+        env->GetLongField(library_info_obj, load_address_id));
+
+    info->load_size = static_cast<size_t>(
+        env->GetLongField(library_info_obj, load_size_id));
+
+    info->relro_start = static_cast<size_t>(
+        env->GetLongField(library_info_obj, relro_start_id));
+
+    info->relro_size = static_cast<size_t>(
+        env->GetLongField(library_info_obj, relro_size_id));
+
+    info->relro_fd = env->GetIntField(library_info_obj, relro_fd_id);
+  }
+
+  void SetLibraryInfo(JNIEnv* env,
+                      jobject library_info_obj,
+                      crazy_library_info_t* info) {
+    env->SetLongField(library_info_obj, load_address_id, info->load_address);
+    env->SetLongField(library_info_obj, load_size_id, info->load_size);
+    env->SetLongField(library_info_obj, relro_start_id, info->relro_start);
+    env->SetLongField(library_info_obj, relro_size_id, info->relro_size);
+    env->SetIntField(library_info_obj, relro_fd_id, info->relro_fd);
+  }
+};
+
+
+static LibInfo_class s_lib_info_fields;
+
+static crazy_context_t* s_crazy_context;
+
+crazy_context_t* GetCrazyContext() {
+  if (!s_crazy_context) {
+    // Create new context.
+    s_crazy_context = crazy_context_create();
+
+    // Ensure libraries located in the same directory than the linker
+    // can be loaded.
+    crazy_context_add_search_path_for_address(
+        s_crazy_context, reinterpret_cast<void*>(&s_crazy_context));
+  }
+
+  return s_crazy_context;
+}
+
+// Load a library with the Chrome linker. This will also call its
+// JNI_OnLoad() method, which shall register its methods. Note that
+// lazy native method resolution will _not_ work after this, because
+// Dalvik uses the system's dlsym() which won't see the new library,
+// so explicit registration is mandatory.
+jboolean nativeLoadLibrary(JNIEnv* env,

[bulach, 2013/09/09 11:43:18]

nit: LoadLibrary, but again, much simpler to just use the JNI generator
machinery..

[digit1, 2013/09/10 09:23:30]

Done.

+                           jclass  clazz,
+                           jstring library_name,
+                           jlong   load_address,
+                           jobject library_info) {
+  String lib_name(env, library_name);
+  const char* UNUSED lib_basename = GetBaseNamePtr(lib_name.c_str());
+
+  crazy_context_t* context = GetCrazyContext();
+
+  // Set the desired load address (0 means randomize it).
+  crazy_context_set_load_address(context,
+                                 static_cast<size_t>(load_address));
+
+  // Open the library now.
+  LOG_INFO("%s: Opening shared library: %s", __FUNCTION__, lib_name.c_str());
+
+  // Not using a ScopedLibrary here is intentional, since leaking
+  // the library, even in case of error, is intentional.
+  crazy_library_t* library;
+  if (!crazy_library_open(&library, lib_name.c_str(), context)) {
+    LOG_ERROR("%s: Could not open %s: %s", __FUNCTION__, lib_basename,
+              crazy_context_get_error(context));
+    return false;
+  }
+
+  if (library_info) {
+    crazy_library_info_t info;
+
+    memset(&info, 0, sizeof(info));
+    info.relro_fd = -1;
+
+    if (!crazy_library_get_info(library, context, &info)) {
+      LOG_INFO("%s: Could not get library info for %s: %s",
+               __FUNCTION__, lib_name.c_str(),
+               crazy_context_get_error(context));
+    } else {
+        s_lib_info_fields.SetLibraryInfo(env, library_info, &info);
+    }
+  }
+
+  LOG_INFO("%s: Looking for JNI_OnLoad() in %s", __FUNCTION__, lib_basename);
+
+  int (*jni_on_load_ptr)(JavaVM*, void*);
+  if (crazy_library_find_symbol(
+        library,
+        "JNI_OnLoad",
+        reinterpret_cast<void**>(&jni_on_load_ptr))) {
+
+    LOG_INFO("%s: Calling JNI_OnLoad() in %s", __FUNCTION__, lib_basename);
+
+    // Call it.
+    int ret = (*jni_on_load_ptr)(s_java_vm, NULL);
+    if (ret < JNI_VERSION_1_4) {
+      LOG_ERROR("%s: JNI_OnLoad() of %s returned %d, at least %d expected",
+                __FUNCTION__, lib_basename, ret, JNI_VERSION_1_4);
+      return false;
+    }
+  }
+
+  LOG_INFO("%s: Success loading library %s", __FUNCTION__, lib_basename);
+  return true;
+}
+
+jboolean nativeEnableSharedRelro(JNIEnv* env,

[bulach, 2013/09/09 11:43:18]

nit: s/native//

[digit1, 2013/09/10 09:23:30]

Done.

+                                 jclass clazz,
+                                 jstring library_name,
+                                 jobject lib_info_obj) {
+  String lib_name(env, library_name);
+
+  LOG_INFO("%s: Called for %s", __FUNCTION__, lib_name.c_str());
+
+  ScopedLibrary library;
+  if (!crazy_library_find_by_name(lib_name.c_str(), library.GetPtr())) {
+    LOG_ERROR("%s: Could not find %s", __FUNCTION__, lib_name.c_str());
+    return false;
+  }
+
+  crazy_context_t* context = GetCrazyContext();
+
+  if (!crazy_library_enable_relro_sharing(library.Get(), context)) {
+    LOG_ERROR("%s: Could not enable RELRO sharing for %s: %s",
+              __FUNCTION__, lib_name.c_str(),
+              crazy_context_get_error(context));
+    return false;
+  }
+
+  crazy_library_info_t info;
+  if (!crazy_library_get_info(library.Get(), context, &info)) {
+    LOG_ERROR("%s: Could not retrieve %s information: %s",
+              __FUNCTION__, lib_name.c_str(),
+              crazy_context_get_error(context));
+    return false;
+  }
+
+  s_lib_info_fields.SetLibraryInfo(env, lib_info_obj, &info);
+  return true;
+}
+
+jboolean nativeUseSharedRelro(JNIEnv* env,
+                              jclass clazz,
+                              jstring library_name,
+                              jobject lib_info_obj) {
+  String lib_name(env, library_name);
+
+  LOG_INFO("%s: called for %s, lib_info_ref=%p",
+           __FUNCTION__, lib_name.c_str(), lib_info_obj);
+
+  ScopedLibrary library;
+  if (!crazy_library_find_by_name(lib_name.c_str(), library.GetPtr())) {
+    LOG_ERROR("%s: Could not find %s", __FUNCTION__, lib_name.c_str());
+    return false;
+  }
+
+  crazy_context_t* context = GetCrazyContext();
+  crazy_library_info_t info;
+  s_lib_info_fields.GetLibraryInfo(env, lib_info_obj, &info);
+
+  LOG_INFO(
+      "%s: library=%s load_addr=%p load_size=%p relro_start=%p relro_size=%p "
+      "relro_fd=%d",
+      __FUNCTION__,
+      lib_name.c_str(),
+      (void*)info.load_address,
+      (void*)info.load_size,
+      (void*)info.relro_start,
+      (void*)info.relro_size,
+      info.relro_fd);
+
+  if (!crazy_library_use_relro_sharing(library.Get(),
+                                       info.relro_start,
+                                       info.relro_size,
+                                       info.relro_fd,
+                                       context)) {
+    LOG_ERROR("%s: Could not enable RELRO sharing for %s: %s",
+            __FUNCTION__, lib_name.c_str(),
+            crazy_context_get_error(context));
+    return false;
+  }
+
+  LOG_INFO("%s: Library %s using shared RELRO section!",
+            __FUNCTION__, lib_name.c_str());
+
+  return true;
+}
+
+static const JNINativeMethod kNativeMethods[] = {
+  { "nativeLoadLibrary",
+    "("
+    "Ljava/lang/String;"
+    "J"
+    "Lorg/chromium/base/Linker$LibInfo;"
+    ")"
+    "Z",
+    reinterpret_cast<void*>(&nativeLoadLibrary) },
+
+  { "nativeEnableSharedRelro",
+    "("
+    "Ljava/lang/String;"
+    "Lorg/chromium/base/Linker$LibInfo;"
+    ")"
+    "Z",
+    reinterpret_cast<void*>(&nativeEnableSharedRelro) },
+
+  { "nativeUseSharedRelro",
+    "("
+    "Ljava/lang/String;"
+    "Lorg/chromium/base/Linker$LibInfo;"
+    ")"
+    "Z",
+    reinterpret_cast<void*>(&nativeUseSharedRelro) },
+};
+
+}  // namespace
+
+jint JNI_OnLoad(JavaVM* vm, void* reserved) {
+  s_java_vm = vm;
+
+  LOG_INFO("%s: Entering", __FUNCTION__);
+  // Get new JNIEnv
+  JNIEnv* env;
+  if (vm->GetEnv(
+          reinterpret_cast<void**>(&env), JNI_VERSION_1_4) != JNI_OK) {

[jar (doing other things), 2013/09/06 17:08:50]

nit: indent seemed strange.  Better might be:

if (JNI_OK != vm->GetEnv(reinterpret_cast<void**>(&env),
                         JNI_VERSION_1_4)) {

[digit1, 2013/09/10 09:23:30]

Done.

+    LOG_ERROR("Could not create JNIEnv");
+    return -1;
+  }
+
+  // Register native methods.
+  jclass linker_class;
+  if (!InitClassReference(env, "org/chromium/base/Linker", &linker_class))
+    return -1;
+
+  LOG_INFO("%s: Registering native methods", __FUNCTION__);
+  env->RegisterNatives(linker_class,
+                       kNativeMethods,
+                       sizeof(kNativeMethods)/sizeof(kNativeMethods[0]));
+
+
+  // Find LibInfo field ids.
+  LOG_INFO("%s: Caching field IDs", __FUNCTION__);
+  if (!s_lib_info_fields.Init(env)) {
+    return -1;
+  }
+
+  LOG_INFO("%s: Done", __FUNCTION__);
+  return JNI_VERSION_1_4;
+}