Android system — 链接器命名空间共享库配置方法（Android 11后）

Android system --- 链接器命名空间共享库配置方法

[1. 应用进程](#1. 应用进程)
- [1.1 应用进程类加载器的命名空间初始化](#1.1 应用进程类加载器的命名空间初始化)
- - [1.1.1 OpenNativeLibrary](#1.1.1 OpenNativeLibrary)
  - [1.1.2 LibraryNamespaces::Create](#1.1.2 LibraryNamespaces::Create)
- [1.2 配置共享库位置](#1.2 配置共享库位置)
[2. native进程](#2. native进程)
- [2.1 native 命名空间配置初始化](#2.1 native 命名空间配置初始化)
- - [2.1.1 android_namespace_t::is_accessible](#2.1.1 android_namespace_t::is_accessible)
  - [2.1.2 init_default_namespaces](#2.1.2 init_default_namespaces)
- [2.2 配置共享库位置](#2.2 配置共享库位置)

1. 应用进程

1.1 应用进程类加载器的命名空间初始化

在应用程序对应的可执行文件app_process根据/linkerconfig/ld.config.txt配置文件初始化命名空间之后，每当应用程序创建一个类加载器classloader并调用System.loadLibrary加载so库时都会创建一个与此类加载器对应的命名空间。从源码角度分析一下这个过程，System.loadLibrary函数最后会调用OpenNativeLibrary函数。

1.1.1 OpenNativeLibrary

System.loadLibrary()-->nativeLoad()-->Runtime.c::Runtime_nativeLoad()-->JVM_NativeLoad()-->Openjdkjvm.cc::JVM_NativeLoad()-->java_vm_ext.cc::LoadNativeLibrary()-->native_loader.cpp::OpenNativeLibrary() 也就是java层的System.loadLibrary()最终会调用libnativeloader.so的OpenNativeLibrary函数。

OpenNativeLibrary先判断classloader类加载器是否为空，如果为空直接调用android_dlopen_ext加载库文件
如果判断classloader类加载器不为空，并且classloader类加载器没有对应的命名空间（第一次调用System.loadLibrary)就调用LibraryNamespaces::Create创建新的命名空间。

cpp 复制代码

void* OpenNativeLibrary(JNIEnv* env, int32_t target_sdk_version, const char* path,
                        jobject class_loader, const char* caller_location, jstring library_path,
                        bool* needs_native_bridge, char** error_msg) {
#if defined(ART_TARGET_ANDROID)
  UNUSED(target_sdk_version);

  if (class_loader == nullptr) { //如果类加载器为空直接调用android_dlopen_ext加载库文件
    *needs_native_bridge = false;
    if (caller_location != nullptr) {
      android_namespace_t* boot_namespace = FindExportedNamespace(caller_location);
      if (boot_namespace != nullptr) {
        const android_dlextinfo dlextinfo = {
            .flags = ANDROID_DLEXT_USE_NAMESPACE,
            .library_namespace = boot_namespace,
        };
        void* handle = android_dlopen_ext(path, RTLD_NOW, &dlextinfo);
        if (handle == nullptr) {
          *error_msg = strdup(dlerror());
        }
        return handle;
      }
    }

    // Check if the library is in NATIVELOADER_DEFAULT_NAMESPACE_LIBS and should
    // be loaded from the kNativeloaderExtraLibs namespace.
    {
      Result<void*> handle = TryLoadNativeloaderExtraLib(path);
      if (!handle.ok()) {
        *error_msg = strdup(handle.error().message().c_str());
        return nullptr;
      }
      if (handle.value() != nullptr) {
        return handle.value();
      }
    }

    // Fall back to the system namespace. This happens for preloaded JNI
    // libraries in the zygote.
    // TODO(b/185833744): Investigate if this should fall back to the app main
    // namespace (aka anonymous namespace) instead.
    void* handle = OpenSystemLibrary(path, RTLD_NOW);
    if (handle == nullptr) {
      *error_msg = strdup(dlerror());
    }
    return handle;
  }

  std::lock_guard<std::mutex> guard(g_namespaces_mutex);
  NativeLoaderNamespace* ns;

  if ((ns = g_namespaces->FindNamespaceByClassLoader(env, class_loader)) == nullptr) { //如果类加载器不为空，且类加载器没有对应的命名空间就新创建一个
    // This is the case where the classloader was not created by ApplicationLoaders
    // In this case we create an isolated not-shared namespace for it.
    Result<NativeLoaderNamespace*> isolated_ns =
        CreateClassLoaderNamespaceLocked(env,
                                         target_sdk_version,
                                         class_loader,
                                         /*is_shared=*/false,
                                         /*dex_path=*/nullptr,
                                         library_path,
                                         /*permitted_path=*/nullptr,
                                         /*uses_library_list=*/nullptr);
    if (!isolated_ns.ok()) {
      *error_msg = strdup(isolated_ns.error().message().c_str());
      return nullptr;
    } else {
      ns = *isolated_ns;
    }
  }

  return OpenNativeLibraryInNamespace(ns, path, needs_native_bridge, error_msg);

在CreateClassLoaderNamespaceLocked中我们可以看到调用了LibraryNamespaces::Create创建新的命名空间

cpp 复制代码

Result<NativeLoaderNamespace*> CreateClassLoaderNamespaceLocked(JNIEnv* env,
                                                                int32_t target_sdk_version,
                                                                jobject class_loader,
                                                                bool is_shared,
                                                                jstring dex_path,
                                                                jstring library_path,
                                                                jstring permitted_path,
                                                                jstring uses_library_list)
    REQUIRES(g_namespaces_mutex) {
  Result<NativeLoaderNamespace*> ns = g_namespaces->Create(env,
                                                           target_sdk_version,
                                                           class_loader,
                                                           is_shared,
                                                           dex_path,
                                                           library_path,
                                                           permitted_path,
                                                           uses_library_list);
  if (!ns.ok()) {
    return ns;
  }
  Result<void> linked = CreateNativeloaderDefaultNamespaceLibsLink(*ns.value());
  if (!linked.ok()) {
    return linked.error();
  }
  return ns;
}

1.1.2 LibraryNamespaces::Create

先调用android_create_namespace创建一个clns命名空间
调用android_linker_namespace设置新创建的命名空间链接到system、APEX和vendor等命名空间
设置链接到system、APEX等命名空间的共享库

cpp 复制代码

Result<NativeLoaderNamespace*> LibraryNamespaces::Create(JNIEnv* env, uint32_t target_sdk_version,
                                                         jobject class_loader, bool is_shared,
                                                         jstring dex_path_j,
                                                         jstring java_library_path,
                                                         jstring java_permitted_path,
                                                         jstring uses_library_list) {
  std::string library_path;  // empty string by default.
  std::string dex_path;

  ......

  // Create the app namespace
  NativeLoaderNamespace* parent_ns = FindParentNamespaceByClassLoader(env, class_loader);
  // Heuristic: the first classloader with non-empty library_path is assumed to
  // be the main classloader for app
  // TODO(b/139178525) remove this heuristic by determining this in LoadedApk (or its
  // friends) and then passing it down to here.
  bool is_main_classloader = app_main_namespace_ == nullptr && !library_path.empty();
  // Policy: the namespace for the main classloader is also used as the
  // anonymous namespace.
  bool also_used_as_anonymous = is_main_classloader;
  // Note: this function is executed with g_namespaces_mutex held, thus no
  // racing here.
  //创建命名空间，namespace_name为kClassloaderNamespaceName = "clns"
  auto app_ns = NativeLoaderNamespace::Create(
      namespace_name, library_path, permitted_path, parent_ns, is_shared,
      target_sdk_version < 24 /* is_exempt_list_enabled */, also_used_as_anonymous);
  if (!app_ns.ok()) {
    return app_ns.error();
  }
  // ... and link to other namespaces to allow access to some public libraries
  bool is_bridged = app_ns->IsBridged();

  auto system_ns = NativeLoaderNamespace::GetSystemNamespace(is_bridged);
  if (!system_ns.ok()) {
    return system_ns.error();
  }
  // 新创建的命名空间链接到system，共享库设置为system_exposed_libraries
  auto linked = app_ns->Link(&system_ns.value(), system_exposed_libraries);
  if (!linked.ok()) {
    return linked.error();
  }

  for (const auto&[apex_ns_name, public_libs] : apex_public_libraries()) {
    auto ns = NativeLoaderNamespace::GetExportedNamespace(apex_ns_name, is_bridged);
    // Even if APEX namespace is visible, it may not be available to bridged.
    if (ns.ok()) {
      // 新创建的命名空间链接到APEX，共享库设置为public_libs
      linked = app_ns->Link(&ns.value(), public_libs);
      if (!linked.ok()) {
        return linked.error();
      }
    }
  }

  // Give access to VNDK-SP libraries from the 'vndk' namespace for unbundled vendor apps.
  if (unbundled_app_origin == APK_ORIGIN_VENDOR && !vndksp_libraries_vendor().empty()) {
    auto vndk_ns = NativeLoaderNamespace::GetExportedNamespace(kVndkNamespaceName, is_bridged);
    if (vndk_ns.ok()) {
      // 新创建的命名空间链接到vndk，共享库设置为vndksp_libraries_vendor()
      linked = app_ns->Link(&vndk_ns.value(), vndksp_libraries_vendor());
      if (!linked.ok()) {
        return linked.error();
      }
    }
  }

  // Give access to VNDK-SP libraries from the 'vndk_product' namespace for unbundled product apps.
  if (unbundled_app_origin == APK_ORIGIN_PRODUCT && !vndksp_libraries_product().empty()) {
    auto vndk_ns = NativeLoaderNamespace::GetExportedNamespace(kVndkProductNamespaceName, is_bridged);
    if (vndk_ns.ok()) {
      linked = app_ns->Link(&vndk_ns.value(), vndksp_libraries_product());
      if (!linked.ok()) {
        return linked.error();
      }
    }
  }

  for (const std::string& each_jar_path : android::base::Split(dex_path, ":")) {
    auto apex_ns_name = FindApexNamespaceName(each_jar_path);
    if (apex_ns_name.ok()) {
      const auto& jni_libs = apex_jni_libraries(*apex_ns_name);
      if (jni_libs != "") {
        auto apex_ns = NativeLoaderNamespace::GetExportedNamespace(*apex_ns_name, is_bridged);
        if (apex_ns.ok()) {
          linked = app_ns->Link(&apex_ns.value(), jni_libs);
          if (!linked.ok()) {
            return linked.error();
          }
        }
      }
    }
  }

  auto vendor_libs = filter_public_libraries(target_sdk_version, uses_libraries,
                                             vendor_public_libraries());
  if (!vendor_libs.empty()) {
    auto vendor_ns = NativeLoaderNamespace::GetExportedNamespace(kVendorNamespaceName, is_bridged);
    // when vendor_ns is not configured, link to the system namespace
    auto target_ns = vendor_ns.ok() ? vendor_ns : system_ns;
    if (target_ns.ok()) {
      linked = app_ns->Link(&target_ns.value(), vendor_libs);
      if (!linked.ok()) {
        return linked.error();
      }
    }
  }

  auto product_libs = filter_public_libraries(target_sdk_version, uses_libraries,
                                              product_public_libraries());
  if (!product_libs.empty()) {
    auto target_ns = system_ns;
    if (is_product_vndk_version_defined()) {
      // If ro.product.vndk.version is defined, product namespace provides the product libraries.
      target_ns = NativeLoaderNamespace::GetExportedNamespace(kProductNamespaceName, is_bridged);
    }
    if (target_ns.ok()) {
      linked = app_ns->Link(&target_ns.value(), product_libs);
      if (!linked.ok()) {
        return linked.error();
      }
    } else {
      // The linkerconfig must have a problem on defining the product namespace in the system
      // section. Skip linking product namespace. This will not affect most of the apps. Only the
      // apps that requires the product public libraries will fail.
      ALOGW("Namespace for product libs not found: %s", target_ns.error().message().c_str());
    }
  }

  auto& emplaced = namespaces_.emplace_back(
      std::make_pair(env->NewWeakGlobalRef(class_loader), *app_ns));
  if (is_main_classloader) {
    app_main_namespace_ = &emplaced.second;
  }
  return &emplaced.second;
}

1.2 配置共享库位置

通过上面的代码跟踪我们会发现，其实在Android 11后，应用进程共享库的配置位置都在public_libraries.cpp中

cpp 复制代码

// art/libnativeloader/public_libraries.cpp
namespace {

constexpr const char* kDefaultPublicLibrariesFile = "/etc/public.libraries.txt";
constexpr const char* kExtendedPublicLibrariesFilePrefix = "public.libraries-";
constexpr const char* kExtendedPublicLibrariesFileSuffix = ".txt";
constexpr const char* kApexLibrariesConfigFile = "/linkerconfig/apex.libraries.config.txt";
constexpr const char* kVendorPublicLibrariesFile = "/vendor/etc/public.libraries.txt";
constexpr const char* kLlndkLibrariesFile = "/apex/com.android.vndk.v{}/etc/llndk.libraries.{}.txt";
constexpr const char* kVndkLibrariesFile = "/apex/com.android.vndk.v{}/etc/vndksp.libraries.{}.txt";

只要在命名空间对应的配置文件中加上自己需要的共享库即可

2. native进程

2.1 native 命名空间配置初始化

native进程的so库是直接通过dlopen打开的，而其对应的命名空间也是直接通过linker进行判断的，并没有调用到libnativeloader.so，因此native进程的配置方式也与应用进程不同

2.1.1 android_namespace_t::is_accessible

前一篇Android system --- 链接器命名空间（linker namespace）源码分析介绍了dlopen时会通过is_accessible进行权限判断

cpp 复制代码

// bionic/linker/linker_namespaces.cpp
// Given an absolute path, can this library be loaded into this namespace?
bool android_namespace_t::is_accessible(const std::string& file) {
  //判断命名空间的is_isolated_，即是否为严格隔离，如果不是则权限检查通过。
  if (!is_isolated_) {
    return true;
  }
  //判断是否在允许名单中
  if (!allowed_libs_.empty()) {
    const char *lib_name = basename(file.c_str());
    if (std::find(allowed_libs_.begin(), allowed_libs_.end(), lib_name) == allowed_libs_.end()) {
      return false;
    }
  }
  //判断是否在ld_library_paths中（LD_LIBRARY_PATH设置）
  for (const auto& dir : ld_library_paths_) {
    if (file_is_in_dir(file, dir)) {
      return true;
    }
  }
  //判断是否在default_library_paths中
  for (const auto& dir : default_library_paths_) {
    if (file_is_in_dir(file, dir)) {
      return true;
    }
  }
  //判断是否在特权路径permitted_paths中
  for (const auto& dir : permitted_paths_) {
    if (file_is_under_dir(file, dir)) {
      return true;
    }
  }

  return false;
}

我们可以看到这里有个allowed_libs_，我们跟踪代码可以发现linker_namespaces.h中有set_allowed_libs接口

cpp 复制代码

// bionic/linker/linker_namespaces.h 
  const std::vector<std::string>& get_allowed_libs() const { return allowed_libs_; }
  void set_allowed_libs(std::vector<std::string>&& allowed_libs) {
    allowed_libs_ = std::move(allowed_libs);
  }
  void set_allowed_libs(const std::vector<std::string>& allowed_libs) {
    allowed_libs_ = allowed_libs;
  }

2.1.2 init_default_namespaces

通过这个思路我们发现调用其实在init_default_namespaces

初始化default命名空间
初始化vndk等其他命名空间
在命名空间之间建立链接

cpp 复制代码

std::vector<android_namespace_t*> init_default_namespaces(const char* executable_path) {
  g_default_namespace.set_name("(default)");

  soinfo* somain = solist_get_somain();

  const char *interp = phdr_table_get_interpreter_name(somain->phdr, somain->phnum,
                                                       somain->load_bias);
  const char* bname = (interp != nullptr) ? basename(interp) : nullptr;

  g_is_asan = bname != nullptr &&
              (strcmp(bname, "linker_asan") == 0 ||
               strcmp(bname, "linker_asan64") == 0);

  const Config* config = nullptr;

  {
    std::string ld_config_file_path = get_ld_config_file_path(executable_path);
    INFO("[ Reading linker config \"%s\" ]", ld_config_file_path.c_str());
    ScopedTrace trace(("linker config " + ld_config_file_path).c_str());
    std::string error_msg;
    if (!Config::read_binary_config(ld_config_file_path.c_str(), executable_path, g_is_asan,
                                    &config, &error_msg)) {
      if (!error_msg.empty()) {
        DL_WARN("Warning: couldn't read '%s' for '%s' (using default configuration instead): %s",
                ld_config_file_path.c_str(), executable_path, error_msg.c_str());
      }
      config = nullptr;
    }
  }

  if (config == nullptr) {
    return init_default_namespace_no_config(g_is_asan);
  }

  const auto& namespace_configs = config->namespace_configs();
  std::unordered_map<std::string, android_namespace_t*> namespaces;

  // 1. Initialize default namespace
  const NamespaceConfig* default_ns_config = config->default_namespace_config();

  g_default_namespace.set_isolated(default_ns_config->isolated());
  g_default_namespace.set_default_library_paths(default_ns_config->search_paths());
  g_default_namespace.set_permitted_paths(default_ns_config->permitted_paths());

  namespaces[default_ns_config->name()] = &g_default_namespace;
  if (default_ns_config->visible()) {
    g_exported_namespaces[default_ns_config->name()] = &g_default_namespace;
  }

  // 2. Initialize other namespaces

  for (auto& ns_config : namespace_configs) {
    if (namespaces.find(ns_config->name()) != namespaces.end()) {
      continue;
    }

    android_namespace_t* ns = new (g_namespace_allocator.alloc()) android_namespace_t();
    ns->set_name(ns_config->name());
    ns->set_isolated(ns_config->isolated());
    ns->set_default_library_paths(ns_config->search_paths());
    ns->set_permitted_paths(ns_config->permitted_paths());
    ns->set_allowed_libs(ns_config->allowed_libs());

    namespaces[ns_config->name()] = ns;
    if (ns_config->visible()) {
      g_exported_namespaces[ns_config->name()] = ns;
    }
  }

  // 3. Establish links between namespaces
  for (auto& ns_config : namespace_configs) {
    auto it_from = namespaces.find(ns_config->name());
    CHECK(it_from != namespaces.end());
    android_namespace_t* namespace_from = it_from->second;
    for (const NamespaceLinkConfig& ns_link : ns_config->links()) {
      auto it_to = namespaces.find(ns_link.ns_name());
      CHECK(it_to != namespaces.end());
      android_namespace_t* namespace_to = it_to->second;
      if (ns_link.allow_all_shared_libs()) {
        link_namespaces_all_libs(namespace_from, namespace_to);
      } else {
        link_namespaces(namespace_from, namespace_to, ns_link.shared_libs().c_str());
      }
    }
  }
  // we can no longer rely on the fact that libdl.so is part of default namespace
  // this is why we want to add ld-android.so to all namespaces from ld.config.txt
  soinfo* ld_android_so = solist_get_head();

  // we also need vdso to be available for all namespaces (if present)
  soinfo* vdso = solist_get_vdso();
  for (auto it : namespaces) {
    if (it.second != &g_default_namespace) {
      it.second->add_soinfo(ld_android_so);
      if (vdso != nullptr) {
        it.second->add_soinfo(vdso);
      }
      // somain and ld_preloads are added to these namespaces after LD_PRELOAD libs are linked
    }
  }

  set_application_target_sdk_version(config->target_sdk_version());

  std::vector<android_namespace_t*> created_namespaces;
  created_namespaces.reserve(namespaces.size());
  for (const auto& kv : namespaces) {
    created_namespaces.push_back(kv.second);
  }
  return created_namespaces;
}
}

这里面我们发现配置文件是通过读取配置文件进行配置的，配置文件ld_config_file_path在Android 11后便改为/linkerconfig/ld.config.txt

cpp 复制代码

static const char* const kLdConfigArchFilePath = "/system/etc/ld.config." ABI_STRING ".txt";

static const char* const kLdConfigFilePath = "/system/etc/ld.config.txt";
static const char* const kLdConfigVndkLiteFilePath = "/system/etc/ld.config.vndk_lite.txt";

static const char* const kLdGeneratedConfigFilePath = "/linkerconfig/ld.config.txt";

static std::string get_ld_config_file_path(const char* executable_path) {
#ifdef USE_LD_CONFIG_FILE
  // This is a debugging/testing only feature. Must not be available on
  // production builds.
  const char* ld_config_file_env = getenv("LD_CONFIG_FILE");
  if (ld_config_file_env != nullptr && file_exists(ld_config_file_env)) {
    return ld_config_file_env;
  }
#endif

  std::string path = get_ld_config_file_apex_path(executable_path);
  if (!path.empty()) {
    if (file_exists(path.c_str())) {
      return path;
    }
    DL_WARN("Warning: couldn't read config file \"%s\" for \"%s\"",
            path.c_str(), executable_path);
  }

  path = kLdConfigArchFilePath;
  if (file_exists(path.c_str())) {
    return path;
  }

  if (file_exists(kLdGeneratedConfigFilePath)) {
    return kLdGeneratedConfigFilePath;
  }

  if (is_linker_config_expected(executable_path)) {
    DL_WARN("Warning: failed to find generated linker configuration from \"%s\"",
            kLdGeneratedConfigFilePath);
  }

  path = get_ld_config_file_vndk_path();
  if (file_exists(path.c_str())) {
    return path;
  }

  return kLdConfigFilePath;
}

2.2 配置共享库位置

上一章我们提到了配置文件位置为/linkerconfig/ld.config.txt，

在Android 11以前ld.config.txt是通过静态文件配置的，而Android 11是改为linkerconfig动态生成

我们以一个vendor/bin下的native 程序为例，要使用system/lib下的库

在Android system --- Android链接器命名空间（Android 11后）中，我们提到了"目录-区段"映射属性dir.name，指向 [name] 区段所应用到的目录的路径，其实就是baseconfig.cc中定义的dirToSection

cpp 复制代码

// system/linkerconfig/contents/configuration/baseconfig.cc

android::linkerconfig::modules::Configuration CreateBaseConfiguration(
    Context& ctx) {
  std::vector<Section> sections;

  ctx.SetCurrentLinkerConfigType(LinkerConfigType::Default);

  // Don't change the order here. The first pattern that matches with the
  // absolute path of an executable is selected.
  std::vector<DirToSection> dirToSection = {
      {"/system/bin/", "system"},
      {"/system/xbin/", "system"},
      {Var("SYSTEM_EXT") + "/bin/", "system"},

      // Processes from the product partition will have a separate section if
      // PRODUCT_PRODUCT_VNDK_VERSION is defined. Otherwise, they are run from
      // the "system" section.
      {Var("PRODUCT") + "/bin/", "product"},

      {"/odm/bin/", "vendor"},
      {"/vendor/bin/", "vendor"},
      {"/data/nativetest/odm", "vendor"},
      {"/data/nativetest64/odm", "vendor"},
      {"/data/benchmarktest/odm", "vendor"},
      {"/data/benchmarktest64/odm", "vendor"},
      {"/data/nativetest/vendor", "vendor"},
      {"/data/nativetest64/vendor", "vendor"},
      {"/data/benchmarktest/vendor", "vendor"},
      {"/data/benchmarktest64/vendor", "vendor"},

      {"/data/nativetest/unrestricted", "unrestricted"},
      {"/data/nativetest64/unrestricted", "unrestricted"},

      // Create isolated namespace for development purpose.
      // This isolates binary from the system so binaries and libraries from
      // this location can be separated from system libraries.
      {"/data/local/tmp/isolated", "isolated"},

      // Create directories under shell-writable /data/local/tests for
      // each namespace in order to run tests.
      {"/data/local/tests/product", "product"},
      {"/data/local/tests/system", "system"},
      {"/data/local/tests/unrestricted", "unrestricted"},
      {"/data/local/tests/vendor", "vendor"},

      // TODO(b/123864775): Ensure tests are run from one of the subdirectories
      // above.  Then clean this up.
      {"/data/local/tmp", "unrestricted"},

      {"/postinstall", "postinstall"},
      // Fallback entry to provide APEX namespace lookups for binaries anywhere
      // else. This must be last.
      {"/data", "system"},
      // TODO(b/168556887): Remove this when we have a dedicated section for
      // binaries in APKs
      {Var("PRODUCT") + "/app/", "system"},
  };

  sections.emplace_back(BuildSystemSection(ctx));
  if (ctx.IsVndkAvailable()) {
    sections.emplace_back(BuildVendorSection(ctx));
    if (android::linkerconfig::modules::IsProductVndkVersionDefined()) {
      sections.emplace_back(BuildProductSection(ctx));
    } else {
      RedirectSection(dirToSection, "product", "system");
    }
  } else {
    RemoveSection(dirToSection, "product");
    RemoveSection(dirToSection, "vendor");
  }

  sections.emplace_back(BuildUnrestrictedSection(ctx));
  sections.emplace_back(BuildPostInstallSection(ctx));

  sections.emplace_back(BuildIsolatedSection(ctx));

  return android::linkerconfig::modules::Configuration(std::move(sections),
                                                       dirToSection);
}

因为我们是vendor/bin下面的程序，所以可以看出来我们是vendor section，因此我们看BuildVendorSection即可。

cpp 复制代码

// system/linkerconfig/contents/section/vendor.cc

Section BuildVendorSection(Context& ctx) {
  ctx.SetCurrentSection(SectionType::Vendor);
  std::vector<Namespace> namespaces;

  namespaces.emplace_back(BuildVendorDefaultNamespace(ctx));
  namespaces.emplace_back(BuildVndkNamespace(ctx, VndkUserPartition::Vendor));
  namespaces.emplace_back(BuildSystemNamespace(ctx));
  namespaces.emplace_back(BuildRsNamespace(ctx));

  if (android::linkerconfig::modules::IsVndkInSystemNamespace()) {
    namespaces.emplace_back(BuildVndkInSystemNamespace(ctx));
  }

  std::set<std::string> visible_apexes;

  // APEXes with public libs should be visible
  for (const auto& apex : ctx.GetApexModules()) {
    if (apex.public_libs.size() > 0) {
      visible_apexes.insert(apex.name);
    }
  }

  android::linkerconfig::modules::LibProviders libs_providers = {};
  if (ctx.IsVndkAvailable()) {
    libs_providers[":vndk"] = android::linkerconfig::modules::LibProvider{
        "vndk",
        std::bind(BuildVndkNamespace, ctx, VndkUserPartition::Vendor),
        {Var("VNDK_SAMEPROCESS_LIBRARIES_VENDOR"),
         Var("VNDK_CORE_LIBRARIES_VENDOR")},
    };
  }

  return BuildSection(
      ctx, "vendor", std::move(namespaces), visible_apexes, libs_providers);
}

我们可以看到最后调用了BuildSection，在其中调用了AddStandardSystemLinks 添加system的共享库

cpp 复制代码

// system/linkerconfig/contents/section/sectionbuilder.cc

Section BuildSection(const Context& ctx, const std::string& name,
                     std::vector<Namespace>&& namespaces,
                     const std::set<std::string>& visible_apexes,
                     const LibProviders& providers) {
  // add additional visible APEX namespaces
  for (const auto& apex : ctx.GetApexModules()) {
    if (visible_apexes.find(apex.name) == visible_apexes.end() &&
        !apex.visible) {
      continue;
    }
    if (auto it = std::find_if(
            namespaces.begin(),
            namespaces.end(),
            [&apex](auto& ns) { return ns.GetName() == apex.namespace_name; });
        it == namespaces.end()) {
      auto ns = ctx.BuildApexNamespace(apex, true);
      namespaces.push_back(std::move(ns));
    } else {
      // override "visible" when the apex is already created
      it->SetVisible(true);
    }
  }

  // resolve provide/require constraints
  Section section(std::move(name), std::move(namespaces));
  if (auto res = section.Resolve(ctx, providers); !res.ok()) {
    LOG(ERROR) << res.error();
  }

  AddStandardSystemLinks(ctx, &section); // 添加通用的system link共享库
  return section;
}

在kBionicLibs 加上我们需要的库即可

cpp 复制代码

 // system/linkerconfig/contents/common/system_links.cc

namespace {
const std::vector<std::string> kBionicLibs = {
    "libc.so",
    "libdl.so",
    "libdl_android.so",
    "libm.so",
};
}  // namespace

namespace android {
namespace linkerconfig {
namespace contents {

using android::linkerconfig::modules::Namespace;
using android::linkerconfig::modules::Section;

void AddStandardSystemLinks(const Context& ctx, Section* section) {
  const bool debuggable = android::base::GetBoolProperty("ro.debuggable", false);
  const std::string system_ns_name = ctx.GetSystemNamespaceName();
  const bool is_section_vndk_enabled = ctx.IsSectionVndkEnabled();
  section->ForEachNamespaces([&](Namespace& ns) {
    if (ns.GetName() != system_ns_name) {
      ns.GetLink(system_ns_name).AddSharedLib(kBionicLibs);
      if (!is_section_vndk_enabled || ns.GetName() != "default") {
        // TODO(b/185199923) remove the default value
        ns.GetLink(system_ns_name)
            .AddSharedLib(Var("SANITIZER_RUNTIME_LIBRARIES", ""));
      }
      if (debuggable) {
        // Library on the system image that can be dlopened for debugging purposes.
        ns.GetLink(system_ns_name).AddSharedLib("libfdtrack.so");
      }
    }
  });
}

}  // namespace contents
}  // namespace linkerconfig
}  // namespace android