ndk学习9: 动态使用共享库
动态使用共享库函数
dll_main
环境介绍
续上节代码
目录结构:
android.mk如下:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := demo
LOCAL_SRC_FILES := mod1.cpp mod2.cpp mod3.cpp
include $(BUILD_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := Hello
LOCAL_SRC_FILES := Hello.cpp
include $(BUILD_EXECUTABLE)
Hello.cpp
#include <stdio.h>
#include <dlfcn.h>
typedef void (*FUNTYPE)();
int main(int argc, char* argv[])
{
//加载共享库
void *handle = dlopen("/data/local/tmp/libdemo.so", RTLD_NOW);
if (handle == NULL)
{
puts(dlerror());
return 0;
}
printf("handle=%p\n", handle);
//获取导出函数
FUNTYPE pfnMod = (FUNTYPE)dlsym(handle, "_Z4mod1v");
if (pfnMod != NULL)
{
printf("address=%p\n", pfnMod);
pfnMod();
}
pfnMod = (FUNTYPE)dlsym(handle, "_Z4mod2v");
if (pfnMod != NULL)
{
printf("address=%p\n", pfnMod);
pfnMod();
}
pfnMod = (FUNTYPE)dlsym(handle, "_Z4mod3v");
if (pfnMod != NULL)
{
printf("address=%p\n", pfnMod);
pfnMod();
}
pfnMod = (FUNTYPE)dlsym(handle, "mod4");
if (pfnMod == NULL)
{
puts(dlerror());
}
dlclose(handle);
return 0;
}
_Z4mod2v 是C++的名称粉碎
函数名可以用readelf来进行查看:
该工具在: E:\Android\android-ndk-r10b\toolchains\x86-4.6\prebuilt\windows-x86_64\bin\i686-linux-android-readelf.exe
类似于Windows动态调用dll的思想
dlopen打开一个so文件
dlsym根据函数名拿到函数指针
编译后使用makefile执行
在工程目录根下新建makefile:
MODALE_NAME := Hello
# x86 path
X86_TOOLS_PATH :=E:\Android\android-ndk-r10b\toolchains\x86-4.6\prebuilt\windows-x86_64\bin
X86_GDB_PATH := $(X86_TOOLS_PATH)\i686-linux-android-gdb.exe
X86_GDB_SERVER := E:\Android\android-ndk-r10b\prebuilt\android-x86\gdbserver\gdbserver
# arm-linux-androideabi-4.6 path
arm_tools_path :=E:\Android\android-ndk-r10b\toolchains\arm-linux-androideabi-4.6\prebuilt\windows-x86_64\bin
arm_4_6_path := $(arm_tools_path)\arm-linux-androideabi-gdb.exe
arm_gdb_server :=E:\Android\android-ndk-r10b\prebuilt\android-arm\gdbserver\gdbserver
run_arm:
adb push .\libs\armeabi-v7a\$(MODALE_NAME) /data/local/tmp
adb shell chmod 755 /data/local/tmp/$(MODALE_NAME)
adb shell /data/local/tmp/$(MODALE_NAME)
run_x86:
adb push .\libs\x86\$(MODALE_NAME) /data/local/tmp
adb shell chmod 755 /data/local/tmp/$(MODALE_NAME)
adb shell /data/local/tmp/$(MODALE_NAME)
run_x86_share:
adb push .\libs\x86\$(MODALE_NAME) /data/local/tmp
adb push .\libs\x86\libdemo.so /data/local/tmp
adb shell chmod 755 /data/local/tmp/$(MODALE_NAME)
adb shell /data/local/tmp/$(MODALE_NAME)
debug_x86:
adb forward tcp:12345 tcp:12345
adb push $(X86_GDB_SERVER) /data/local/tmp
adb shell chmod 777 /data/local/tmp/gdbserver
adb push .\obj\local\x86\$(MODALE_NAME) /data/local/tmp
adb shell chmod 777 /data/local/tmp/$(MODALE_NAME)
adb shell /data/local/tmp/gdbserver :12345 /data/local/tmp/$(MODALE_NAME)
client_x86:
$(X86_GDB_PATH) .\obj\local\x86\$(MODALE_NAME)
# 1. target remote localhost:12345
# 2. gdb.setup
make run_x86_share 即可成功执行
mod4 会提示找不到
DLL_MAIN
修改mod1.cpp
#include <stdio.h>
// 初始化函数
void _init()
{
printf("_init\r\n");
}
// so卸载函数
void _fini()
{
printf("_fini\r\n");
}
// 新版本初始化函数
void __attribute__((constructor)) OnLoad()
{
printf("OnLoad\r\n");
}
void __attribute__((destructor)) UnLoad()
{
printf("UnLoad\r\n");
}
void __attribute__((constructor)) OnLoad2()
{
printf("OnLoad2\r\n");
}
void __attribute__((destructor)) UnLoad2()
{
printf("UnLoad2\r\n");
}
//隐藏函数
void __attribute__((visibility("hidden"))) mod1()
{
printf("mod1\r\n");
}
运行效果:
说明:
1. _init函数比构造函数来的早
2. hidden后在用dlsym函数无法找到
总结:
1.相关函数
dlopen()函数打开一个共享库
dlsym()函数在库中搜索一个符号
dlclose() 函数光比之前dlopen打开的库
dlerror() 函数返回一个错误消息的字符串
2.隐藏函数
Void __attribute__ ((visibility("hidden"))) fun() {}
3. so构造析构(会在so加载和卸载的时候调用)
void __attribute__ ((constructor)) Load()
void __attribute__ ((destructor)) UnLoad()
4. _init()和_fini()函数
会在so加载和卸载时调用
