Android模拟器学framework和driver之传感器篇3（Android HAL）

dwlinux_gs 2014-07-25

展开全文

前面，带着大家一起写了一个temperature sensor的驱动，已经一个测试tool来测试这个驱动，基本功能已经ok，若还有问题的可以参考前面2篇文章，在这里我们要在HAL层中添加我们的设备，来跟framework中的代码连接起来。

在开始摆代码之前我觉得有必要啰嗦几句，HAL层我个人觉得是个比较重要的东西，虽然这边现在还不是很成熟，还不是很规范，但是google还是做了很大力气针对HAL的。

首先来介绍一下android HAL 层，

Android的硬件抽象层，简单来说，就是对Linux内核驱动程序的封装，向上提供接口，屏蔽低层的实现细节。也就是说，把对硬件的支持分成了两层，一层放在用户空间（User Space），一层放在内核空间（Kernel Space），其中，硬件抽象层运行在用户空间，而Linux内核驱动程序运行在内核空间。
下图为整个android 架构：

这个是google定义的android整个系统的架构，大家可以看到HAL层起了一个承上启下的作用，HAL层主要是针对一些传感器和一些个硬件而存在的，其实也可以绕过HAL层直接使用JNI来实现从驱动到framework这个过程，但是我们这里主要是讲android中的sensor，针对标准的android而言，sensor都是在HAL中添加的，个人理解还是呼应硬件厂商的建议吧，毕竟这部分代码还可以不开源的。

好了，开源不开源什么的，我是不去关心，对我影响不大，我们还是接着看HAL。

Android硬件抽象层，从下到上涉及到了Android系统的硬件驱动层、硬件抽象层、运行时库和应用程序框架层等等，下图描述了硬件抽象层在Android系统中的位置，以及它和其它层的关系：

现在的libhardware 作法，使用了stub的概念。stub 虽然仍是以*.so 檔的形式存在，但HAL 已经将*.so 档隐藏起来了。Stub 向HAL提供操作函数（operations），而runtime 则是向HAL 取得特定模块（stub）的operations，再callback 这些操作函数。
HAL的实现主要在hardware.c和hardware.h文件中。实质也是通过加载*.so 库。从而呼叫*.so 里的符号（symbol）实现。

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到此，都是些理论的东西，实在是不想讲这些条条杠杠的，从小语文就不好的我，最讨厌的就是这些理论的东西了，实践才是真理呢。。。

好了接下来轮到我们的sensor的HAL层了，这里先列出来主要用到的代码：

。。。。。。

讲漏了，这边sensor的HAL层代码我参考的是freescale的BSP，因为个人感觉比较容易懂，哈哈。

先给下载链接，不然大家看不到完整的代码。

http://download.csdn.net/detail/zhangjie201412/4039312

代码目录如下：

sensor/
├──AccelSensor.cpp
├──AccelSensor.h
├──Android.mk
├──InputEventReader.cpp
├──InputEventReader.h
├──LightSensor.cpp
├──LightSensor.h
├──SensorBase.cpp
├──SensorBase.h
├──sensors.cpp
├──sensors.h
├──TemperatureSensor.cpp
└──TemperatureSensor.h

这里我们要修改以及添加的是三个文件：

sensor.cpp TemperatureSensor.cpp TemperatureSensor.h

好了，接下来就带大家分析下android sensor的HAL层！！！

先看一下/hardware/libhareware/hardware.c和/hardware/libhardware/include/hardware/hardware.h

这2个文件是android hal层最重要的两个文件，其中定义了hal层主要要实现的3个结构体，

struct hw_module_t;
struct hw_module_methods_t;
struct hw_device_t;

/**
* 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.
*/
typedef struct hw_module_t {
    /** tag must be initialized to HARDWARE_MODULE_TAG */
    uint32_t tag;

    /** major version number for the module */
    uint16_t version_major;

    /** minor version number of the module */
    uint16_t version_minor;

    /** Identifier of module */
    const char *id;

    /** Name of this module */
    const char *name;

    /** Author/owner/implementor of the module */
    const char *author;

    /** Modules methods */
    struct hw_module_methods_t* methods;

    /** module's dso */
    void* dso;

    /** padding to 128 bytes, reserved for future use */
    uint32_t reserved[32-7];

} hw_module_t;

typedef struct hw_module_methods_t {
    /** Open a specific device */
    int (*open)(const struct hw_module_t* module, const char* id,
            struct hw_device_t** device);

} hw_module_methods_t;

/**
* Every device data structure must begin with hw_device_t
* followed by module specific public methods and attributes.
*/
typedef struct hw_device_t {
    /** tag must be initialized to HARDWARE_DEVICE_TAG */
    uint32_t tag;

    /** version number for hw_device_t */
  uint32_t version;

    /** reference to the module this device belongs to */
    struct hw_module_t* module;

    /** padding reserved for future use */
    uint32_t reserved[12];

    /** Close this device */
    int (*close)(struct hw_device_t* device);

} hw_device_t;
struct hw_module_t;
struct hw_module_methods_t;
struct hw_device_t;

/**
* 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.
*/
typedef struct hw_module_t {
    /** tag must be initialized to HARDWARE_MODULE_TAG */
    uint32_t tag;

    /** major version number for the module */
    uint16_t version_major;

    /** minor version number of the module */
    uint16_t version_minor;

    /** Identifier of module */
    const char *id;

    /** Name of this module */
    const char *name;

    /** Author/owner/implementor of the module */
    const char *author;

    /** Modules methods */
    struct hw_module_methods_t* methods;

    /** module's dso */
    void* dso;

    /** padding to 128 bytes, reserved for future use */
    uint32_t reserved[32-7];

} hw_module_t;

typedef struct hw_module_methods_t {
    /** Open a specific device */
    int (*open)(const struct hw_module_t* module, const char* id,
            struct hw_device_t** device);

} hw_module_methods_t;

/**
* Every device data structure must begin with hw_device_t
* followed by module specific public methods and attributes.
*/
typedef struct hw_device_t {
    /** tag must be initialized to HARDWARE_DEVICE_TAG */
    uint32_t tag;

    /** version number for hw_device_t */
    uint32_t version;

    /** reference to the module this device belongs to */
    struct hw_module_t* module;

    /** padding reserved for future use */
    uint32_t reserved[12];

    /** Close this device */
    int (*close)(struct hw_device_t* device);

} hw_device_t;
其实标准的android hal就是实现这3个结构体，然后设置一些回调函数，最后把数据poll到framework中。

好，接下来看下sensor中是怎么封装的：

在/hardware/libhardware/include/hardware/sensors.h 中定义了几个结构体，其中都包含了上面的3个结构体，所以我们sensor module只需要去实现sensor.h中的这几个就OK了。

下面提一下如何添加我们的temperature sensor，首先是hardware/libhardware/modules/sensor/sensors.cpp 中sensor list中添加我们的sensor的信息，

/* The SENSORS Module */
static const struct sensor_t sSensorList[] = {
        { "Analog Devices ADXL345/6 3-axis Accelerometer",
          "ADI",
          1, SENSORS_ACCELERATION_HANDLE,
          SENSOR_TYPE_ACCELEROMETER, RANGE_A, CONVERT_A, 0.145f, 200, { } },    //20000
        { "Android Light sensor",
          "Android",
          1, SENSORS_LIGHT_HANDLE,
          SENSOR_TYPE_LIGHT, 16000.0f, 1.0f, 0.35f, 0, { } },
    //++++++add by Jay for temperature sensor
    { "Android Temperature Sensor",
      "Android",
      1, SENSORS_TEMPERATURE_HANDLE,
      SENSOR_TYPE_TEMPERATURE, 100.0f, 1.0f, 1.0f,0, { }},
    //-----------
};
/* The SENSORS Module */
static const struct sensor_t sSensorList[] = {
        { "Analog Devices ADXL345/6 3-axis Accelerometer",
          "ADI",
          1, SENSORS_ACCELERATION_HANDLE,
          SENSOR_TYPE_ACCELEROMETER, RANGE_A, CONVERT_A, 0.145f, 200, { } },       //20000
        { "Android Light sensor",
          "Android",
          1, SENSORS_LIGHT_HANDLE,
          SENSOR_TYPE_LIGHT, 16000.0f, 1.0f, 0.35f, 0, { } },
       //++++++add by Jay for temperature sensor
       { "Android Temperature Sensor",
       "Android",
       1, SENSORS_TEMPERATURE_HANDLE,
       SENSOR_TYPE_TEMPERATURE, 100.0f, 1.0f, 1.0f,0, { }},
       //-----------
};这里面的Android Temperature Sensor就是我们自己添加的sensor，然后我们去实现我们的temperature sensor的功能，也就是填充一些结构体和实现一些回调函数，这里我挑重要的讲。

int TemperatureSensor::readEvents(sensors_event_t* data, int count)
{
    if(count<1)
        return -EINVAL;

    if(mHasPendingEvent){
        mHasPendingEvent = false;
        mPendingEvent.timestamp = getTimestamp();
        *data = mPendingEvent;
        return mEnabled ? 1:0;
    }
    ssize_t n = mInputReader.fill(data_fd);
    if(n<0)
        return n;

    int numEventReceived = 0;
    input_event const* event;
    DEBUG("count: %d\n",count);
    while(count && mInputReader.readEvent(&event)){
        int fd=open("/dev/input/event1", O_RDONLY);
        if(fd<0){
            DEBUG("readEvents: open event2 failed...\n");
            return fd;
        }
        int ret=read(fd,&event,sizeof(event));
      if(ret<sizeof(event)){
            DEBUG("readEvent read failed....\n");
            return ret;
        }
        close(fd);
        int type=event->type;
        if(type == EV_ABS){
            DEBUG("Current Temp: %d\n",event->value);
            mPendingEvent.temperature = (float)(event->value);
        }else if(type==EV_SYN){
            mPendingEvent.timestamp = timevalToNano(event->time);
            if(/*mEnabled &&*/ (mPendingEvent.temperature != mPreviousTemperature)){
                *data++ = mPendingEvent;
                count--;
                numEventReceived++;
                mPreviousTemperature = mPendingEvent.temperature;
                DEBUG("Current Temp: %d\n",(int)mPendingEvent.temperature);
            }
        }else
            DEBUG("temperature : unknow event...\n");
        mInputReader.next();
    }
    return numEventReceived;
}
int TemperatureSensor::readEvents(sensors_event_t* data, int count)
{
       if(count<1)
              return -EINVAL;

       if(mHasPendingEvent){
              mHasPendingEvent = false;
              mPendingEvent.timestamp = getTimestamp();
              *data = mPendingEvent;
              return mEnabled ? 1:0;
       }
       ssize_t n = mInputReader.fill(data_fd);
       if(n<0)
              return n;

       int numEventReceived = 0;
       input_event const* event;
       DEBUG("count: %d\n",count);
       while(count && mInputReader.readEvent(&event)){
              int fd=open("/dev/input/event1", O_RDONLY);
              if(fd<0){
                     DEBUG("readEvents: open event2 failed...\n");
                     return fd;
              }
              int ret=read(fd,&event,sizeof(event));
              if(ret<sizeof(event)){
                     DEBUG("readEvent read failed....\n");
                     return ret;
              }
              close(fd);
              int type=event->type;
              if(type == EV_ABS){
                     DEBUG("Current Temp: %d\n",event->value);
                     mPendingEvent.temperature = (float)(event->value);
              }else if(type==EV_SYN){
                     mPendingEvent.timestamp = timevalToNano(event->time);
                     if(/*mEnabled &&*/ (mPendingEvent.temperature != mPreviousTemperature)){
                            *data++ = mPendingEvent;
                            count--;
                            numEventReceived++;
                            mPreviousTemperature = mPendingEvent.temperature;
                            DEBUG("Current Temp: %d\n",(int)mPendingEvent.temperature);
                     }
              }else
                     DEBUG("temperature : unknow event...\n");
              mInputReader.next();
       }
       return numEventReceived;
}大家看了Temperature.cpp就应该知道我这里实现HAL层poll数据最主要的就是上面这个函数，这边其实就是linux的应用层的写法，open input 节点，然后read data，在poll给framework层。

这里我要提醒大家，如果对自己不够有信心的话第一次写hal层代码的时候最好多加点debug message，因为在hal层的调试比较麻烦，出现的错误会直接导致系统不断重启，不会告诉你错哪，所以，最好自己加debug message来调试。

代码方面大家可以看下Temperature.h和sensor.cpp这两个文件里面要实现的一些类和结构体，按照规范写好回调函数就ok了，大家自行分析绰绰有余。

还有就是这里的makefile，会把module编译成sensor.goldfish.so，给framework调用，ok来讲一下framework是如何调用HAL层里面的API的，

大家可以看下android源码下面的frameworks/base/services/sensorservice/SensorDevice.cpp

SensorDevice::SensorDevice()
    : mSensorDevice(0),
       mSensorModule(0)
{
    status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
            (hw_module_t const**)&mSensorModule);

    LOGE_IF(err, "couldn't load %s module (%s)",
            SENSORS_HARDWARE_MODULE_ID, strerror(-err));

    if (mSensorModule) {
        err = sensors_open(&mSensorModule->common, &mSensorDevice);

        LOGE_IF(err, "couldn't open device for module %s (%s)",
                SENSORS_HARDWARE_MODULE_ID, strerror(-err));

        if (mSensorDevice) {
            sensor_t const* list;
            ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);
            mActivationCount.setCapacity(count);
            Info model;
            for (size_t i=0 ; i<size_t(count) ; i++) {
                mActivationCount.add(list[i].handle, model);
                mSensorDevice->activate(mSensorDevice, list[i].handle, 0);
            }
        }
    }
}
SensorDevice::SensorDevice()
    : mSensorDevice(0),
       mSensorModule(0)
{
    status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
            (hw_module_t const**)&mSensorModule);

    LOGE_IF(err, "couldn't load %s module (%s)",
            SENSORS_HARDWARE_MODULE_ID, strerror(-err));

    if (mSensorModule) {
        err = sensors_open(&mSensorModule->common, &mSensorDevice);

        LOGE_IF(err, "couldn't open device for module %s (%s)",
                SENSORS_HARDWARE_MODULE_ID, strerror(-err));

        if (mSensorDevice) {
            sensor_t const* list;
            ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);
            mActivationCount.setCapacity(count);
            Info model;
            for (size_t i=0 ; i<size_t(count) ; i++) {
                mActivationCount.add(list[i].handle, model);
                mSensorDevice->activate(mSensorDevice, list[i].handle, 0);
            }
        }
    }
}

这里调用了status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
            (hw_module_t const**)&mSensorModule);
status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
            (hw_module_t const**)&mSensorModule);

这个函数在哪呢？在这：

hardware/libhardware/hardware.c里的

int hw_get_module(const char *id, const struct hw_module_t **module)
{
    int status;
    int i;
    const struct hw_module_t *hmi = NULL;
    char prop[PATH_MAX];
    char path[PATH_MAX];

    /*
     * Here we rely on the fact that calling dlopen multiple times on
     * the same .so will simply increment a refcount (and not load
     * a new copy of the library).
     * We also assume that dlopen() is thread-safe.
     */

    /* Loop through the configuration variants looking for a module */
    for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
        if (i < HAL_VARIANT_KEYS_COUNT) {
            if (property_get(variant_keys[i], prop, NULL) == 0) {
                continue;
            }
            snprintf(path, sizeof(path), "%s/%s.%s.so",
                    HAL_LIBRARY_PATH1, id, prop);
            if (access(path, R_OK) == 0) break;

            snprintf(path, sizeof(path), "%s/%s.%s.so",
                     HAL_LIBRARY_PATH2, id, prop);
            if (access(path, R_OK) == 0) break;
        } else {
            snprintf(path, sizeof(path), "%s/%s.default.so",
                     HAL_LIBRARY_PATH1, id);
            if (access(path, R_OK) == 0) break;
        }
    }

    status = -ENOENT;
    if (i < HAL_VARIANT_KEYS_COUNT+1) {
        /* load the module, if this fails, we're doomed, and we should not try
         * to load a different variant. */
        status = load(id, path, module);
    }

    return status;
}
int hw_get_module(const char *id, const struct hw_module_t **module)
{
    int status;
    int i;
    const struct hw_module_t *hmi = NULL;
    char prop[PATH_MAX];
    char path[PATH_MAX];

    /*
     * Here we rely on the fact that calling dlopen multiple times on
     * the same .so will simply increment a refcount (and not load
     * a new copy of the library).
     * We also assume that dlopen() is thread-safe.
     */

    /* Loop through the configuration variants looking for a module */
    for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
        if (i < HAL_VARIANT_KEYS_COUNT) {
            if (property_get(variant_keys[i], prop, NULL) == 0) {
                continue;
            }
            snprintf(path, sizeof(path), "%s/%s.%s.so",
                    HAL_LIBRARY_PATH1, id, prop);
            if (access(path, R_OK) == 0) break;

            snprintf(path, sizeof(path), "%s/%s.%s.so",
                     HAL_LIBRARY_PATH2, id, prop);
            if (access(path, R_OK) == 0) break;
        } else {
            snprintf(path, sizeof(path), "%s/%s.default.so",
                     HAL_LIBRARY_PATH1, id);
            if (access(path, R_OK) == 0) break;
        }
    }

    status = -ENOENT;
    if (i < HAL_VARIANT_KEYS_COUNT+1) {
        /* load the module, if this fails, we're doomed, and we should not try
         * to load a different variant. */
        status = load(id, path, module);
    }

    return status;
}

这里首先把要get的module的名字传进去，然后找到sensor.goldfish.so，但是怎么去加载这个binary呢？

看下这里的load函数：

/**
* Load the file defined by the variant and if successful
* return the dlopen handle and the hmi.
* @return 0 = success, !0 = failure.
*/
static int load(const char *id,
        const char *path,
        const struct hw_module_t **pHmi)
{
    int status;
    void *handle;
    struct hw_module_t *hmi;

    /*
     * load the symbols resolving undefined symbols before
     * dlopen returns. Since RTLD_GLOBAL is not or'd in with
     * RTLD_NOW the external symbols will not be global
     */
    handle = dlopen(path, RTLD_NOW);
    if (handle == NULL) {
        char const *err_str = dlerror();
        LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");
        status = -EINVAL;
        goto done;
    }

    /* Get the address of the struct hal_module_info. */
    const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
    hmi = (struct hw_module_t *)dlsym(handle, sym);
    if (hmi == NULL) {
        LOGE("load: couldn't find symbol %s", sym);
        status = -EINVAL;
        goto done;
    }

    /* Check that the id matches */
    if (strcmp(id, hmi->id) != 0) {
        LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
        status = -EINVAL;
        goto done;
    }

    hmi->dso = handle;

    /* success */
    status = 0;

    done:
    if (status != 0) {
        hmi = NULL;
        if (handle != NULL) {
            dlclose(handle);
            handle = NULL;
        }
    } else {
        LOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
                id, path, *pHmi, handle);
    }

    *pHmi = hmi;

    return status;
}
/**
* Load the file defined by the variant and if successful
* return the dlopen handle and the hmi.
* @return 0 = success, !0 = failure.
*/
static int load(const char *id,
        const char *path,
        const struct hw_module_t **pHmi)
{
    int status;
    void *handle;
    struct hw_module_t *hmi;

    /*
     * load the symbols resolving undefined symbols before
     * dlopen returns. Since RTLD_GLOBAL is not or'd in with
     * RTLD_NOW the external symbols will not be global
     */
    handle = dlopen(path, RTLD_NOW);
    if (handle == NULL) {
        char const *err_str = dlerror();
        LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");
        status = -EINVAL;
        goto done;
    }

    /* Get the address of the struct hal_module_info. */
    const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
    hmi = (struct hw_module_t *)dlsym(handle, sym);
    if (hmi == NULL) {
        LOGE("load: couldn't find symbol %s", sym);
        status = -EINVAL;
        goto done;
    }

    /* Check that the id matches */
    if (strcmp(id, hmi->id) != 0) {
        LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
        status = -EINVAL;
        goto done;
    }

    hmi->dso = handle;

    /* success */
    status = 0;

    done:
    if (status != 0) {
        hmi = NULL;
        if (handle != NULL) {
            dlclose(handle);
            handle = NULL;
        }
    } else {
        LOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
                id, path, *pHmi, handle);
    }

    *pHmi = hmi;

    return status;
}

handle = dlopen(path, RTLD_NOW)；这个函数是用来打开找到的sensor.goldfish.so这个动态库的，然后找到这个库里的一些回调函数，怎么找呢？
handle = dlopen(path, RTLD_NOW)；这个函数是用来打开找到的sensor.goldfish.so这个动态库的，然后找到这个库里的一些回调函数，怎么找呢？看下这句话：
看下这句话：<pre name="code" class="cpp" style="background-color: rgb(255, 255, 255); "><pre name="code" class="cpp">    /* Get the address of the struct hal_module_info. */
    const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
<pre name="code" class="cpp" style="background-color: rgb(255, 255, 255); "><pre name="code" class="cpp">    /* Get the address of the struct hal_module_info. */
    const char *sym = HAL_MODULE_INFO_SYM_AS_STR;

HAL_MODULE_INFO_SYM_AS_STR;是一个宏，被定义在hardware.h中：
HAL_MODULE_INFO_SYM_AS_STR;是一个宏，被定义在hardware.h中：<pre name="code" class="cpp">#define HAL_MODULE_INFO_SYM_AS_STR "HMI"
<pre name="code" class="cpp">#define HAL_MODULE_INFO_SYM_AS_STR "HMI"好了，就是找HMI这个字串，我们可以用readelf命令查看下sensor.glodfish.so里面的symbol：

<pre name="code" class="cpp">root@jay:/home/jay/android/android2.3.3# readelf -s out/target/product/generic/system/lib/hw/sensors.goldfish.so

Symbol table '.dynsym' contains 118 entries:
   Num:    Value Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE LOCAL DEFAULT UND
     1: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_unwind_cpp_pr0
     2: 00001a29    44 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
     3: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_f2iz
     4: 00001a5d   364 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
     5: 00000000     0 FUNC    GLOBAL DEFAULT UND poll
     6: 00000000     0 FUNC    GLOBAL DEFAULT UND __errno
     7: 00000000     0 FUNC    GLOBAL DEFAULT UND strerror
     8: 00000000     0 FUNC    GLOBAL DEFAULT UND __android_log_print
     9: 00000000     0 FUNC    GLOBAL DEFAULT UND read
    10: 00001bd1   120 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    11: 00000000     0 FUNC    GLOBAL DEFAULT UND write
    12: 00001c51    42 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    13: 00000000     0 FUNC    GLOBAL DEFAULT UND close
    14: 00000000     0 FUNC    GLOBAL DEFAULT UND _ZdlPv
    15: 00001c95    42 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    16: 00001cc1   216 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    17: 00000000    0 FUNC    GLOBAL DEFAULT UND _Znwj
    18: 00002455   124 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorC1Ev
    19: 00002af1   288 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorC1Ev
    20: 00002fd5   108 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorC1E
    21: 00000000     0 FUNC    GLOBAL DEFAULT UND pipe
    22: 00000000     0 FUNC    GLOBAL DEFAULT UND fcntl
    23: 00000000     0 FUNC    GLOBAL DEFAULT UND memset
    24: 00001ded   216 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    25: 0000432c   132 OBJECT GLOBAL DEFAULT   16 HMI
    26: 00001ec5    24 FUNC    GLOBAL DEFAULT    7 _ZNK10SensorBase5getFdEv
    27: 00001edd     4 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase8setDelayE
    28: 00001ee1     4 FUNC   GLOBAL DEFAULT    7 _ZNK10SensorBase16hasPend
    29: 00001ee5    32 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase12close_de
    30: 00001f05    60 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseD1Ev
    31: 000040e8    36 OBJECT GLOBAL DEFAULT   13 _ZTV10SensorBase
    32: 00001f41    60 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseD2Ev
    33: 00001f7d   312 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase9openInput
    34: 00000000     0 FUNC    GLOBAL DEFAULT UND opendir
    35: 00000000     0 FUNC    GLOBAL DEFAULT UND strcpy
    36: 00000000     0 FUNC    GLOBAL DEFAULT UND strlen
    37: 00000000     0 FUNC    GLOBAL DEFAULT UND open
    38: 00000000     0 FUNC    GLOBAL DEFAULT UND ioctl
    39: 00000000     0 FUNC    GLOBAL DEFAULT UND strcmp
    40: 00000000     0 FUNC    GLOBAL DEFAULT UND readdir
    41: 00000000     0 FUNC    GLOBAL DEFAULT UND closedir
    42: 00000000     0 FUNC    GLOBAL DEFAULT UND __stack_chk_fail
   43: 00000000     0 OBJECT GLOBAL DEFAULT UND __stack_chk_guard
    44: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_unwind_cpp_pr1
    45: 000020b5    68 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseC1EPKcS1_
    46: 000020f9    68 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseC2EPKcS1_
    47: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_lmul
    48: 00002141    56 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase12getTimes
    49: 00000000     0 FUNC    GLOBAL DEFAULT UND clock_gettime
    50: 00002179    80 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase11open_dev
    51: 000021c9    18 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseD0Ev
    52: 00000000     0 FUNC    GLOBAL DEFAULT UND __cxa_pure_virtual
    53: 000021dd     4 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensor8setDelay
    54: 000021e1    24 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensor6enableEi
    55: 000021f9    12 FUNC    GLOBAL DEFAULT    7 _ZNK11LightSensor16hasPen
    56: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_i2f
    57: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_fcmpeq
    58: 00002209   432 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensor10readEve
    59: 00000000     0 FUNC    GLOBAL DEFAULT UND memcpy
    60: 000030dd    96 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    61: 000030c5    24 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    62: 000030ad    22 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    63: 000023b9    68 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorD1Ev
    64: 0000313d    18 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    65: 00004110    36 OBJECT GLOBAL DEFAULT   13 _ZTV11LightSensor
    66: 000023fd    18 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorD0Ev
    67: 00002411    68 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorD2Ev
    68: 00003165    30 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    69: 000024d1   124 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorC2Ev
    70: 0000254d    48 FUNC   GLOBAL DEFAULT    7 _ZN11AccelSensor6enableEi
    71: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_fmul
    72: 0000257d   120 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor12process
    73: 000025f9   308 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor10readEve
    74: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_ldivmod
    75: 00002731   216 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor8setDelay
    76: 00000000     0 FUNC    GLOBAL DEFAULT UND fopen
    77: 00000000     0 FUNC    GLOBAL DEFAULT UND snprintf
    78: 00000000     0 FUNC    GLOBAL DEFAULT UND fwrite
    79: 00000000     0 FUNC    GLOBAL DEFAULT UND fclose
    80: 00002809   628 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor11getPoll
    81: 00000000     0 FUNC    GLOBAL DEFAULT UND strncmp
    82: 00000000     0 FUNC    GLOBAL DEFAULT UND strcat
    83: 00000000     0 FUNC    GLOBAL DEFAULT UND fread
    84: 00000000     0 FUNC    GLOBAL DEFAULT UND strtol
    85: 00002a7d    48 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorD1Ev
    86: 00004138    36 OBJECT GLOBAL DEFAULT   13 _ZTV11AccelSensor
    87: 00002aad    18 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorD0Ev
    88: 00002ac1    48 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorD2Ev
    89: 00002c11   288 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorC2Ev
    90: 00002d31     4 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensor8se
    91: 00002d35    24 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensor6en
    92: 00002d4d    12 FUNC   GLOBAL DEFAULT    7 _ZNK17TemperatureSensor16
    93: 00002d59   488 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensor10r
    94: 00002f41    64 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorD1E
    95: 00004160    36 OBJECT GLOBAL DEFAULT   13 _ZTV17TemperatureSensor
    96: 00002f81    18 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorD0E
    97: 00002f95    64 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorD2E
    98: 00003041   108 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorC2E
    99: 00000000     0 FUNC    GLOBAL DEFAULT UND _ZdaPv
   100: 00003151    18 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
   101: 00000000     0 FUNC    GLOBAL DEFAULT UND _Znaj
   102: 00003185    30 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
   103: 00000000     0 FUNC    GLOBAL DEFAULT UND __cxa_finalize
   104: 000043c0     0 NOTYPE GLOBAL DEFAULT   17 __dso_handle
   105: 00004000     0 NOTYPE GLOBAL DEFAULT   11 __INIT_ARRAY__
   106: 00004008     0 NOTYPE GLOBAL DEFAULT   12 __FINI_ARRAY__
   107: 000035dc     0 NOTYPE GLOBAL DEFAULT ABS __exidx_start
   108: 0000371c     0 NOTYPE GLOBAL DEFAULT ABS __exidx_end
   109: 0000432c     0 NOTYPE GLOBAL DEFAULT   16 __data_start
   110: 000043b4     0 NOTYPE GLOBAL DEFAULT ABS _edata
   111: 000043b4     0 NOTYPE GLOBAL DEFAULT ABS __bss_start
   112: 000043b4     0 NOTYPE GLOBAL DEFAULT ABS __bss_start__
   113: 000043d0     0 NOTYPE GLOBAL DEFAULT ABS _bss_end__
   114: 000043d0     0 NOTYPE GLOBAL DEFAULT ABS __bss_end__
   115: 000043d0     0 NOTYPE GLOBAL DEFAULT ABS __end__
   116: 000043d0     0 NOTYPE GLOBAL DEFAULT ABS _end
   117: 00080000     0 NOTYPE GLOBAL DEFAULT ABS _stack
<pre name="code" class="cpp">root@jay:/home/jay/android/android2.3.3# readelf -s out/target/product/generic/system/lib/hw/sensors.goldfish.so

Symbol table '.dynsym' contains 118 entries:
   Num:    Value Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE LOCAL DEFAULT UND
     1: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_unwind_cpp_pr0
     2: 00001a29    44 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
     3: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_f2iz
     4: 00001a5d   364 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
     5: 00000000     0 FUNC    GLOBAL DEFAULT UND poll
     6: 00000000     0 FUNC    GLOBAL DEFAULT UND __errno
     7: 00000000     0 FUNC    GLOBAL DEFAULT UND strerror
     8: 00000000     0 FUNC    GLOBAL DEFAULT UND __android_log_print
     9: 00000000     0 FUNC    GLOBAL DEFAULT UND read
    10: 00001bd1   120 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    11: 00000000     0 FUNC    GLOBAL DEFAULT UND write
    12: 00001c51    42 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    13: 00000000     0 FUNC    GLOBAL DEFAULT UND close
    14: 00000000     0 FUNC    GLOBAL DEFAULT UND _ZdlPv
    15: 00001c95    42 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    16: 00001cc1   216 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    17: 00000000     0 FUNC    GLOBAL DEFAULT UND _Znwj
    18: 00002455   124 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorC1Ev
    19: 00002af1   288 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorC1Ev
    20: 00002fd5   108 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorC1E
    21: 00000000     0 FUNC    GLOBAL DEFAULT UND pipe
    22: 00000000     0 FUNC    GLOBAL DEFAULT UND fcntl
    23: 00000000     0 FUNC    GLOBAL DEFAULT UND memset
    24: 00001ded   216 FUNC    GLOBAL DEFAULT    7 _ZN22sensors_poll_context
    25: 0000432c   132 OBJECT GLOBAL DEFAULT   16 HMI
    26: 00001ec5    24 FUNC    GLOBAL DEFAULT    7 _ZNK10SensorBase5getFdEv
    27: 00001edd     4 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase8setDelayE
    28: 00001ee1     4 FUNC    GLOBAL DEFAULT    7 _ZNK10SensorBase16hasPend
    29: 00001ee5    32 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase12close_de
    30: 00001f05    60 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseD1Ev
    31: 000040e8    36 OBJECT GLOBAL DEFAULT   13 _ZTV10SensorBase
    32: 00001f41    60 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseD2Ev
    33: 00001f7d   312 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase9openInput
    34: 00000000     0 FUNC    GLOBAL DEFAULT UND opendir
    35: 00000000     0 FUNC    GLOBAL DEFAULT UND strcpy
    36: 00000000     0 FUNC    GLOBAL DEFAULT UND strlen
    37: 00000000     0 FUNC    GLOBAL DEFAULT UND open
    38: 00000000     0 FUNC    GLOBAL DEFAULT UND ioctl
    39: 00000000     0 FUNC    GLOBAL DEFAULT UND strcmp
    40: 00000000     0 FUNC    GLOBAL DEFAULT UND readdir
    41: 00000000     0 FUNC   GLOBAL DEFAULT UND closedir
    42: 00000000     0 FUNC    GLOBAL DEFAULT UND __stack_chk_fail
    43: 00000000     0 OBJECT GLOBAL DEFAULT UND __stack_chk_guard
    44: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_unwind_cpp_pr1
    45: 000020b5    68 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseC1EPKcS1_
    46: 000020f9    68 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseC2EPKcS1_
    47: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_lmul
    48: 00002141    56 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase12getTimes
    49: 00000000     0 FUNC    GLOBAL DEFAULT UND clock_gettime
    50: 00002179    80 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBase11open_dev
    51: 000021c9    18 FUNC    GLOBAL DEFAULT    7 _ZN10SensorBaseD0Ev
    52: 00000000     0 FUNC    GLOBAL DEFAULT UND __cxa_pure_virtual
    53: 000021dd     4 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensor8setDelay
    54: 000021e1    24 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensor6enableEi
    55: 000021f9    12 FUNC    GLOBAL DEFAULT    7 _ZNK11LightSensor16hasPen
    56: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_i2f
    57: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_fcmpeq
    58: 00002209   432 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensor10readEve
    59: 00000000     0 FUNC    GLOBAL DEFAULT UND memcpy
    60: 000030dd    96 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    61: 000030c5    24 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    62: 000030ad    22 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    63: 000023b9    68 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorD1Ev
    64: 0000313d    18 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    65: 00004110    36 OBJECT GLOBAL DEFAULT   13 _ZTV11LightSensor
    66: 000023fd    18 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorD0Ev
    67: 00002411    68 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorD2Ev
    68: 00003165    30 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
    69: 000024d1   124 FUNC    GLOBAL DEFAULT    7 _ZN11LightSensorC2Ev
    70: 0000254d    48 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor6enableEi
    71: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_fmul
    72: 0000257d   120 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor12process
    73: 000025f9   308 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor10readEve
    74: 00000000     0 FUNC    GLOBAL DEFAULT UND __aeabi_ldivmod
    75: 00002731   216 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor8setDelay
    76: 00000000     0 FUNC    GLOBAL DEFAULT UND fopen
    77: 00000000     0 FUNC    GLOBAL DEFAULT UND snprintf
    78: 00000000     0 FUNC    GLOBAL DEFAULT UND fwrite
    79: 00000000     0 FUNC    GLOBAL DEFAULT UND fclose
    80: 00002809   628 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensor11getPoll
    81: 00000000     0 FUNC    GLOBAL DEFAULT UND strncmp
    82: 00000000     0 FUNC    GLOBAL DEFAULT UND strcat
    83: 00000000     0 FUNC    GLOBAL DEFAULT UND fread
    84: 00000000     0 FUNC    GLOBAL DEFAULT UND strtol
    85: 00002a7d    48 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorD1Ev
    86: 00004138    36 OBJECT GLOBAL DEFAULT   13 _ZTV11AccelSensor
    87: 00002aad    18 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorD0Ev
    88: 00002ac1    48 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorD2Ev
    89: 00002c11   288 FUNC    GLOBAL DEFAULT    7 _ZN11AccelSensorC2Ev
    90: 00002d31     4 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensor8se
    91: 00002d35    24 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensor6en
    92: 00002d4d    12 FUNC    GLOBAL DEFAULT    7 _ZNK17TemperatureSensor16
    93: 00002d59   488 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensor10r
    94: 00002f41    64 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorD1E
    95: 00004160    36 OBJECT GLOBAL DEFAULT   13 _ZTV17TemperatureSensor
    96: 00002f81    18 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorD0E
    97: 00002f95    64 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorD2E
    98: 00003041   108 FUNC    GLOBAL DEFAULT    7 _ZN17TemperatureSensorC2E
    99: 00000000     0 FUNC    GLOBAL DEFAULT UND _ZdaPv
   100: 00003151    18 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
   101: 00000000     0 FUNC    GLOBAL DEFAULT UND _Znaj
   102: 00003185    30 FUNC    GLOBAL DEFAULT    7 _ZN24InputEventCircularRe
   103: 00000000     0 FUNC    GLOBAL DEFAULT UND __cxa_finalize
   104: 000043c0     0 NOTYPE GLOBAL DEFAULT   17 __dso_handle
   105: 00004000     0 NOTYPE GLOBAL DEFAULT   11 __INIT_ARRAY__
   106: 00004008     0 NOTYPE GLOBAL DEFAULT   12 __FINI_ARRAY__
   107: 000035dc     0 NOTYPE GLOBAL DEFAULT ABS __exidx_start
   108: 0000371c     0 NOTYPE GLOBAL DEFAULT ABS __exidx_end
   109: 0000432c     0 NOTYPE GLOBAL DEFAULT   16 __data_start
   110: 000043b4     0 NOTYPE GLOBAL DEFAULT ABS _edata
   111: 000043b4     0 NOTYPE GLOBAL DEFAULT ABS __bss_start
   112: 000043b4     0 NOTYPE GLOBAL DEFAULT ABS __bss_start__
   113: 000043d0     0 NOTYPE GLOBAL DEFAULT ABS _bss_end__
   114: 000043d0     0 NOTYPE GLOBAL DEFAULT ABS __bss_end__
   115: 000043d0     0 NOTYPE GLOBAL DEFAULT ABS __end__
   116: 000043d0     0 NOTYPE GLOBAL DEFAULT ABS _end
   117: 00080000     0 NOTYPE GLOBAL DEFAULT ABS _stack
大家可以看到这里的第25行，OK 找到了，这里找到了这个动态库的地址，然后就可以一次找到这个动态库中的函数，最终可以被调用。

结束语：

这里我只是大致分析了一下这个流程，对于代码是如何编写的，大家可以参考我提供的下载，其实android hal层就是填充一些“规则”。
这里我只是大致分析了一下这个流程，对于代码是如何编写的，大家可以参考我提供的下载，其实android hal层就是填充一些“规则”。下面一节我们来编写一个测试apk来抓我们的温度，之后再来分析framework层，因为到这里我们sensor的移植就结束了，framework层中android已经帮我们把api都写好了，也就是说sensor是android的标准api，我们不需要自己去搭建。

摘自 zhangjie201412的专栏