关于Android import-module 和NDK_MODULE_PATH

缺乏、安全感 2022-08-09 11:44 10阅读 0赞

===========================

一、将NDK代码模块化

二、导出一个预编译库

===========================

一、将NDK代码模块化

Android module paths (sharing code made easy):

Android模块路径（方便共享代码）：

==============================================

Starting from r5, the Android NDK comes with a cool feature that allows you to share and reuse other people's modules more easily.

从r5开始，Android NDK引入一个很酷的特性，允许你更容易地共享和重用他人的模块。

I. Overview:

一、概述：

\------------

The main idea behind this feature are:

这个特性背后的主要思想：

- You can install NDK modules outside of your main project source tree.

- 你可以在你的主工程源码树以外安装NDK模块

- You can easily 'import' them into your project with a one-line command.

- 你可以用一个单行命令简单地“导入”它们到你的工程。

In practice, here's how this works:

实际上，这里介绍它是如何工作的：

1. Your NDK\_MODULE\_PATH environment variable will contain a list of search paths on your system to lookup for modules.

1. 你的NDK\_MODULE\_PATH环境变量将包含一个在你的系统上查找模块的搜索路径列表。

It is up to you to set the variable, and to copy other modules to the directories you listed in it.

由你来决定设置变量和复制你在其中列出的目录下的其他模块。

2. To import a module, place a line like the following to, preferably at the \*end\* of, your Android.mk:

2. 要想导入一个模块，放置如下所示的一行指令，最好放在你的Android.mk文件结束处：

$(call import-module,<tag>)

This will look for <tag>/Android.mk under any of the directories listed in your NDK\_MODULE\_PATH.

这将查找在你的NDK\_MODULE\_PATH中列出的任意目录下的<tag>/Android.mk

(The reason why it must be at the end is to avoid messing with the results of the 'my-dir' function. See its description in docs/ANDROID-MK.html for details).

（它必须放在结束处的理由是为了避免my-dir函数结果的干扰。详细请参考docs/ANDROID-MK.html中的描述）。

3. Declare that your project's modules depend on the imported one by listing them in either your LOCAL\_STATIC\_LIBRARIES or LOCAL\_SHARED\_LIBRARIES. For example:

3. 通过在你的LOCAL\_STATIC\_LIBRARIES或LOCAL\_SHARED\_LIBRARIES中列出它们，声明你的工程模块依赖于这个导入模块。例如：

LOCAL\_STATIC\_LIBRARIES += <tag>

4. Rebuild!

4. 重新构建！

Remember that NDK r5 also added the ability for a module to "export" declarations to other modules that depend on it (for example, see the definition of LOCAL\_EXPORT\_CFLAGS in docs/ANDROID-MK.html).

记住NDK r5还添加模块的能力以“导出”声明到其它依赖于它的模块（例如，参考docs/ANDROID-MK.html中LOCAL\_EXPORT\_CFLAGS的定义）

A well-written module will correctly export all the things its dependees need, et voila.

一个书写良好的模块将正确地导出它的被依赖者所需要的所有东西，就是这样子（注：et voila是法语）。

Now for the full details:

现在是完全的细节：

I. NDK\_MODULE\_PATH:

一、NDK\_MODULE\_PATH：

\-------------------

The NDK\_MODULE\_PATH variable must contain a list of directories.

NDK\_MODULE\_PATH变量必须包含一个目录列表。

\* Due to GNU Make limitations, NDK\_MODULE\_PATH must not contain any space. The NDK will complain if this is not the case.

\* 由于GNU Make的限制，NDK\_MODULE\_PATH不准包含任何空格。NDK将解释它是否违背要求。

\* Use ':' as the path separator.

\* 使用分号作为路径分隔符。

\* On Windows, use '/' as the directory separator.

\* 在Windows上，使用正斜杠作为目录分隔符（注：应该是指把Windows风格的反斜杠改为正斜杠）。

The directories of NDK\_MODULE\_PATH will be searched in order. The first <path>/<tag>/Android.mk file that is found during the lookup will be included automatically.

NDK\_MODULE\_PATH的目录将被依次搜索。第一个在查找种被找到的<path>/<tag>/Android.mk文件将自动被包含。

As a convenience, $NDK/sources is appended to your NDK\_MODULE\_PATH definition by the NDK build system. This allows you to easily import the helper libraries that come with it (see docs/CPU-FEATURES.html for a practical example).

作为约定，$NDK/sources被NDK构建系统尾加到你的NDK\_MODULE\_PATH定义中。这允许你简单地导入由它生成的辅助库（见docs/CPU-FEATURES.html中的一个实际例子）

II. Writing an import module:

二、书写一个导入模块：

\-----------------------------

Writing an import module is trivial and very similar to what you do when writing project modules:

书写一个导入模块是细小而且非常类似于你在书写工程模块时所做的东西：

1. Create a sub-directory from one of your NDK\_MODULE\_PATH directories.

1. 在你的NDK\_MODULE\_PATH目录中的一个目录下创建子目录。

For example, if NDK\_MODULE\_PATH is defined to /home/user/ndk-modules, then create the directory /home/user/ndk-modules/my-module/

例如，如果NDK\_MODULE\_PATH被定义为/home/user/ndk-modules，那么创建目录/home/user/ndk-modules/my-module/

2. Place an Android.mk and eventual source code there.

2. 在那里放置一个Android.mk和最终源码。

Just like you would for a project module, where these files normally go to $PROJECT\_PATH/Android.mk. In the example above, this would go to /home/user/ndk-modules/my-module/Android.mk

就像你对一个工程模块那样，这些文件通常去到$PROJECT\_PATH/Android.mk中。在上面的例子中，它将集中到/home/user/ndk-modules/my-module/Android.mk

NOTE: Any Application.mk file here will be ignored.

注意：这里任何Application.mk文件将被忽略。

3. Any module that depends on your new module, would import by calling the import-module function. For example:

3. 依赖于你的新模块的任何模块，将通过调用import-module函数进行导入。例如：

$(call import-module,my-first-module)

Import modules \*can\* import other modules, but circular dependencies are not permitted and will be detected. Dependencies are transitive and the build system will compute all the things that need to be built for you.

导入模块可以导入其他模块，但不允许循环依赖，它会被检测到。依赖是及物的，构建系统将为你计算所有需要被构建的所有东西。

The NDK build system will not place object files or executables in your import module directory (they will all be placed under the project's build directory, e.g. $PROJECT\_PATH/obj/).

NDK构建系统将不会在你的导入模块目录中放置对象文件或可执行文件（它们将全部放在工程的构建目录下，例如$PROJECT\_PATH/obj/）

You can however distribute prebuilt binaries in your import module with the new PREBUILT\_STATIC\_LIBRARIES or PREBUILT\_SHARED\_LIBRARIES feature (see docs/ANDROID-MK.html).

然而你可以通过新的PREBUILT\_STATIC\_LIBRARIES或PREBUILT\_SHARED\_LIBRARIES特性，在你的导入模块中分发预构建二进制文件（见docs/ANDROID-MK.html）。

This makes it easy to package and redistribute your import module directory to third-parties.

这将使打包和重新分发你的导入模块目录到第三方变得简单。

III. Naming an import module:

三、命名一个导入模块：

\-----------------------------

It is important to understand a few things related to the naming of your import module:

重要是要理解关于你的导入模块命名的一些事情：

- What 'import-module' does is really search for a file named Android.mk using the list provided by NDK\_MODULE\_PATH, then include while performing very little bit of house-keeping.

- import-module所做的实际上是使用NDK\_MODULE\_PATH提供的列表搜索名为Android.mk的文件，然后当执行非常小量的内部工作时包含它。

Your imported Android.mk can define any number of modules, with any name. As a consequence, there is no direct relationship between <name> in the following line:

你的导入Android.mk可以通过名称定义任意数量的模块。因此，在下面指令行中<name>之间不会有直接的关联：

$(call import-module,<tag>/<name>)

And the names of the modules defined under <tag>/<name>/Android.mk.

以及定义在<tag>/<name>/Android.mk下的模块名称。

IN CASE OF DOUBT, KEEP IT SIMPLE!

如果还是不明白，就让它保持简单！

If you only plan to provide one import module, just name it like the base import directory.

如果你只是计划提供一个导入模块，只要像导入基目录那样命名它就可以了。

On the other hand, you may want to provide a static and a shared version of your module: use distinct names under the same top-level Android.mk. Consider the following build script:

另一方面，你可能像提供你的模块的静态和动态版本：在相同的顶级Android.mk下使用不同的名称。考虑以下构建脚本：

$NDK\_MODULE\_PATH/foo/bar/Android.mk:

LOCAL\_PATH := $(call my-dir)

\# Static version of the library is named 'bar\_static'

\# 库的静态版本被命名为bar\_static

include $(CLEAR\_VARS)

LOCAL\_MODULE := bar\_static

LOCAL\_SRC\_FILES := bar.c

\# Ensure our dependees can include <bar.h> too

\# 确保我们的被依赖者还可以包含<bar.h>

LOCAL\_EXPORT\_C\_INCLUDES := $(LOCAL\_PATH)

include $(BUILD\_STATIC\_LIBRARY)

\# Shared version of the library is named 'bar\_shared'

\# 库的动态版被命名为bar\_shared

LOCAL\_MODULE := bar\_shared

LOCAL\_SRC\_FILES := bar.c

LOCAL\_EXPORT\_C\_INCLUDES := $(LOCAL\_PATH)

include $(BUILD\_SHARED\_LIBRARY)

Another module would refer to it by doing the following:

另一个模块将通过以下方法引用它：

1. Import 'foo/bar', as in:

1. 导入foo/bar，像这样：

$(call import-module,foo/bar)

2. To use the static library:

2. 要使用静态库：

...

LOCAL\_STATIC\_LIBRARIES := bar\_static

3. Or to use the shared library:

3. 或者要使用动态库：

...

LOCAL\_SHARED\_LIBRARIES := bar\_shared

- The module namespace is flat, so try to give your modules names that are likely to not collide with other. Note that your can use LOCAL\_MODULE\_FILENAME to give the name of your module's binary file, independently from its LOCAL\_MODULE (see docs/ANDROID-MK.html for definition and usage). For example:

- 模块的命名空间是平的，所以尝试给你的模块一个不可能和其它模块名称冲突的名字。注意你可以使用LOCAL\_MODULE\_FILENAME设置你的模块的二进制文件的名称，独立于LOCAL\_MODULE（见docs/ANDROID-MK.html获得其定义和用法）。例如：

include $(CLEAR\_VARS)

LOCAL\_MODULE := super\_foo

LOCAL\_MODULE\_FILENAME := foo   \# will give libfoo.so \# 将给定为libfoo.so

LOCAL\_SRC\_FILES := foo-src.c

LOCAL\_CFLAGS := -DVOLUME=11

include $(BUILD\_SHARED\_LIBRARY)

include $(CLEAR\_VARS)

LOCAL\_MODULE := normal\_foo

LOCAL\_MODULE\_FILENAME := foo   \# will also give libfoo.so \# 还将给定为libfoo.so

LOCAL\_SRC\_FILES := foo-src.c

include $(BUILD\_SHARED\_LIBRARY)

Defines two modules named "super\_foo" and "normal\_foo" which both produce a shared library named 'libfoo.so'

定义两个模块，名为super\_foo和normal\_foo，它们都将产生一个名为libfoo.so的动态库。

As a consequence, only one of them can be used by your project or a conflict will happen at build time. This allows you to select either the normal or optimized version in your NDK build scripts, while keeping the same simple loading instruction in your Java sources as:

因此，只有它们其中一个可以被你的工程使用或者在构建期发生冲突。这允许你用你的NDK构建脚本选择正常或者优化版本，保持在你的Java源代码中这样子的相同而且简单的加载指令：

static \{

System.loadLibrary("foo");

IV. Tips & Recommendations:

四、提示和建议：

\---------------------------

\* You don't need to import a module before you can reference it!

\* 你不需要在你可以引用它前导入模块！

\* Use import-module at the \*end\* of your Android.mk to avoid messing with the result of 'my-dir'. See the description of this function in docs/ANDROID-MK.html to understand why.

\* 在你的Android.mk结束处使用import-module以避免my-dir结果的干扰。参考docs/ANDROID-MK.html中这个函数的描述以理解为什么。

\* It is \*strongly\* suggested to use a subdirectory for your import tags, that describes its origin, as in:

\* 强烈建议对你的导入标签使用子目录，以描述它的来源，像这样子：

$(call import-module,gtk/glib)

or something like:

或者类似这样：

$(call import-module,com.example/awesomelib)

IMPORTANT: THE 'android' IMPORT DIRECTORY, AND ANY OF ITS SUB-DIRECTORIES IS \*RESERVED\* FOR NDK USAGE. FEEL FREE TO ORGANIZE YOUR OTHER IMPORT MODULES AS YOU WANT OTHERWISE.

重要：“android”导入目录，以及它的任意子目录因为NDK的使用而保留。但是欢迎你按照自己的意愿组织其它导入模块。

二、导出一个预编译库

NDK Prebuilt library support:

NDK 预构建库支持：

\-----------------------------

Android NDK r5 introduced support for prebuilt libraries (shared and static), i.e. the ability to include and use, in your applications, prebuilt version of libraries.

Android NDK r5引入预构建库（动态和静态）的支持，即在你的应用程序中包含和使用库的预构建版本。

This feature can be useful for two things:

这个特性可能在两方面有用：

1/ You want to distribute your own libraries to third-party NDK developers without distributing your sources.

1、你想发布你自己的库给第三方NDK开发者而不分发你的源代码。

2/ You want to use a prebuilt version of your own libraries to speed up your build.

2、你想使用你自己的库的预构建版本以加速你的构建。

This document explains how this support works.

这个文档解释这种支持是如何工作的。

I. Declaring a prebuilt library module:

一、声明一个预构建库模块：

\---------------------------------------

Each prebuilt library must be declared as a \*single\* independent module to the build system. Here is a trivial example where we assume that the file "libfoo.so" is located in the same directory than the Android.mk below:

每个预构建库必须向构建系统声明为一个单一独立模块。这里有个小示例，我们假设文件libfoo.so位于以下Android.mk相同的目录中。

LOCAL\_PATH := $(call my-dir)

include $(CLEAR\_VARS)

LOCAL\_MODULE := foo-prebuilt

LOCAL\_SRC\_FILES := libfoo.so

include $(PREBUILT\_SHARED\_LIBRARY)

Notice that, to declare such a module, you really only need the following:

注意，要声明这个模块，你实际上只需要以下东西：

1. Give the module a name (here 'foo-prebuilt'). This does not need to correspond to the name of the prebuilt library itself.

1. 给模块一个名称（这里是foo-prebuilt）。不需要对应预构建库本身的名称。

2. Assign to LOCAL\_SRC\_FILES the path to the prebuilt library you are providing. As usual, the path is relative to your LOCAL\_PATH.

2. 把你提供的预构建库的路径赋给LOCAL\_SRC\_FILES。通常路径相对于你的LOCAL\_PATH

IMPORTANT: You \*must\* ensure that the prebuilt library corresponds to the target ABI you are using. More on this later.

重要：你必须确保预构建库对应你正在使用的目标ABI（注：应用程序二进制接口，即操作系统开放给应用程序的接口）。更多相关信息见后。

3. Include PREBUILT\_SHARED\_LIBRARY, instead of BUILD\_SHARED\_LIBRARY, if you are providing a shared, library. For static ones, use PREBUILT\_STATIC\_LIBRARY.

3. 包含PREBUILT\_SHARED\_LIBRARY，而非BUILD\_SHARED\_LIBRARY，如果你提供的是一个动态库。对于静态库，请使用PREBUILT\_STATIC\_LIBRARY

A prebuilt module does not build anything. However, a copy of your prebuilt shared library will be copied into $PROJECT/obj/local, and another will be copied and stripped into $PROJECT/libs/<abi>.

一个预构建模块不编译任何东西。然而，你的预构建动态库的副本将被复制到$PROJECT/obj/local，而另一个副本将被复制并裁剪进$PROJECT/libs/<abi>。

II. Referencing the prebuilt library in other modules:

二、引用其它模块的预构建库：

\------------------------------------------------------

Simply list your prebuilt module's name in the LOCAL\_STATIC\_LIBRARIES or LOCAL\_SHARED\_LIBRARIES declaration in the Android.mk of any module that depends on them.

在依赖于你的构建模块的所有模块的Android.mk的LOCAL\_STATIC\_LIBRARIES或LOCAL\_SHARED\_LIBRARIES的声明中简单列出这些预构建模块的名称。

For example, a naive example of a module using libfoo.so would be:

例如，一个使用libfoo.so的模块的单纯例子将是：

include $(CLEAR\_VARS)

LOCAL\_MODULE := foo-user

LOCAL\_SRC\_FILES := foo-user.c

LOCAL\_SHARED\_LIBRARY := foo-prebuilt

include $(BUILD\_SHARED\_LIBRARY)

III. Exporting headers for prebuilt libraries:

三、导出预构建库的头文件：

\----------------------------------------------

The example above was called 'naive' because, in practice, the code in foo-user.c is going to depend on specific declarations that are normally found in a header file distributed with the prebuilt library (e.g. "foo.h").

上面的例子被称为“单纯”是因为，实际上，foo-user.c的代码将依赖于特定的声明，那些声明通常在预构建库分发的头文件中找到（例如，foo.h）

In other words, foo-user.c is going to have a line like:

换句话说，foo-user.c将有类似的一行：

\#include <foo.h>

And you need to provide the header and its include path to the compiler when building the foo-user module.

而你需要在构建foo-user模块时提供头文件和它的编译器包含目录。

A simple way to deal with that is to use exports in the prebuilt module definition. For example, assuming that a file "foo.h" is located under the 'include' directory relative to the prebuilt module, we can write:

一个简单处理方法是在预构建模块定义中使用导出。例如，假设一个foo.h文件位于相对于预构建模块的include目录下，我们可以这样写：

include $(CLEAR\_VARS)

LOCAL\_MODULE := foo-prebuilt

LOCAL\_SRC\_FILES := libfoo.so

LOCAL\_EXPORT\_C\_INCLUDES := $(LOCAL\_PATH)/include

include $(PREBUILT\_SHARED\_LIBRARY)

The LOCAL\_EXPORT\_C\_INCLUDES definition here ensures that any module that depends on the prebuilt one will have its LOCAL\_C\_INCLUDES automatically prepended with the path to the prebuilt's include directory, and will thus be able to find headers inside that.

这里LOCAL\_EXPORT\_C\_INCLUDES的定义确保任何依赖于预构建模块的模块将自动拥有带预构建库包含目录为前置值的LOCAL\_C\_INCLUDES，而它将能够找到包含其中的头文件。

IV. Debugging prebuilt binaries:

四、调试预构建二进制文件：

\--------------------------------

We recommend you to provide prebuilt shared libraries that contain debug symbols. The version that is installed into $PROJECT/libs/<abi>/ is always stripped by the NDK build system, but the debug version will be used for debugging purposes with ndk-gdb.

我们建议你提供包含调试符号的预构建共享库。安装进$PROJECT/libs/<abi>/的版本常常是被NDK构建系统裁剪过（注：ndk提供的工具链中包含了strip工具，它应该是用来优化生成文件的大小），但调试版本将可以供ndk-gdb使用以达到调试目的。

V. ABI Selection of prebuilt binaries:

五、预构建二进制文件的ABI选择：

\--------------------------------------

As said previously, it is crucial to provide a prebuilt shared library that is compatible with the targetted ABI during the build. To do that, check for the value of TARGET\_ARCH\_ABI, its value will be:

正如前面所说，关键问题是在构建期间提供一个兼容于目标ABI的预构建动态库（注：开源是好事啊）。为了做到那点，检查TARGET\_ARCH\_ABI的值，它的值将是：

armeabi     => when targetting ARMv5TE or higher CPUs

armeabi     => 目标为ARMv5TE或更高的CPU

armeabi-v7a => when targetting ARMv7 or higher CPUs

armeabi-v7a => 目标为ARMv7或更高的CPU

x86         => when targetting x86 CPUs

x86         => 目标为x86 CPU。

Note that armeabi-v7a systems can run armeabi binaries just fine.

注意armeabi-v7a系统可以很好地运行armeabi的二进制文件。

Here's an example where we provide two versions of a prebuilt library and select which one to copy based on the target ABI:

这里有一个例子，我们提供两个版本的预构建库并且基于目标ABI选择哪一个版本去复制。

include $(CLEAR\_VARS)