Android HAL层简要分析

最新推荐文章于 2025-04-26 18:37:06 发布

Kitty_London

最新推荐文章于 2025-04-26 18:37:06 发布

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分类专栏： Android系统文章标签： Android

本文链接：https://blog.youkuaiyun.com/Kitty_Landon/article/details/69453317

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本文深入探讨了Android硬件抽象层（HAL）的新框架，重点关注Hal Stub的结构体，包括hw_module_methods_t和hw_device_t。通过分析，揭示了如何通过dlopen和dlsym从SO库中获取硬件对象，以及HAL Stub代码生成的so库命名和位置规则。

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新的HAL框架

新的框架使用的是module stub方式，stub在Binder机制中表示对象引用。应用层加载so库（so库代码我们称之为module），在HAL层注册了每个硬件对象的引用stub，当上层需要访问硬件的时候，就从当前注册的硬件引用对象stub里查找，找到之后stub会向上层module提供该硬件对象的操作接口，该操作接口就保存在module中，应用层再通过这个module操作接口来访问硬件。框架图如下：

Hal Stub框架分析

Hal Stub的框架比较简单，主要记住三个结构体、两个常量、一个函数，简称321架构，定义在：

/hardware/libhardware/include/hardware/hardware.h;

/hardware/libhardware/hardware.c。

三个结构体

struct hw_module_t;
struct hw_module_methods_t;
struct hw_device_t;

先看下hw_modult_t结构体：

/**
 * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
 * and the fields of this data structure must begin with hw_module_t
 * followed by module specific information.每个硬件模块必须有一个以HAL_MODULE_INFO_SYM命名的数据结构；数据结构必须以hw_module_t开始，用来指定module信息。
 */
typedef struct hw_module_t {
    /** tag must be initialized to HARDWARE_MODULE_TAG */
    uint32_t tag;//标签必须初始化为HARDWARE_MODULT_TAG

    /**
     * The API version of the implemented module. The module owner is
     * responsible for updating the version when a module interface has
     * changed.
     *
     * The derived modules such as gralloc and audio own and manage this field.
     * The module user must interpret the version field to decide whether or
     * not to inter-operate with the supplied module implementation.
     * For example, SurfaceFlinger is responsible for making sure that
     * it knows how to manage different versions of the gralloc-module API,
     * and AudioFlinger must know how to do the same for audio-module API.
     *
     * The module API version should include a major and a minor component.
     * For example, version 1.0 could be represented as 0x0100. This format
     * implies that versions 0x0100-0x01ff are all API-compatible.
     *
     * In the future, libhardware will expose a hw_get_module_version()
     * (or equivalent) function that will take minimum/maximum supported
     * versions as arguments and would be able to reject modules with
     *

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