update: android jni

README.md

@@ -28,6 +28,9 @@
 
 * [Hotfix-knowledge-patch](/android/hotfix.md)
 
+* [JNI-practice](/android/jni-practice.md)
+
+
 #### 系统
 
 * [App启动流程](https://www.yuque.com/isaac-laugu/qpc3mv/sux09ah6d6y9vklk)

android/jni-practice.md

@@ -0,0 +1,148 @@
+# 实现一个JNI工程
+
+> Edit at 2023-08-1
+
+## 创建Jni工程
+
+File->new Project->native c++
+
+## 实现本地方法
+### 动态注册
+[link](https://juejin.cn/post/6844904192780271630#heading-37)
+
+每一级文件目录下（每一个文件目录需要有一个CmakeLists配置文件），
+.c/.cpp文件内重写 JNI_OnLoad()函数.
+
+```
+cpp:
+
+
+jint JNI_OnLoad(JavaVM* vm, void* reserved){
+    JNIEnv* env = NULL;
+    // 1. 获取 JNIEnv，这个地方要注意第一个参数是个二级指针
+    int result = vm->GetEnv(reinterpret_cast<void **>(&env), JNI_VERSION_1_6);
+    // 2. 是否获取成功
+    if(result != JNI_OK){
+        ALOG("获取 env 失败");
+        return JNI_VERSION_1_6;
+    }
+    // 3. 注册方法
+    //HOOK_JNI_CLASS_NAME 为Java调用jni方法的路径，例如："com/jni/senthinkprivate/Utils/HookUtils"
+    jclass classMainActivity = (env)->FindClass(HOOK_JNI_CLASS_NAME);
+
+    //关联Java方法与native方法
+    JNINativeMethod m[] = {
+            {"hookString", "()V", (void*)test},
+//            {"nativeHook", "(I)I", (void*)hacker_hook},
+    };
+
+    // sizeof(methods)/ sizeof(JNINativeMethod)
+    result = env->RegisterNatives(classMainActivity,m, sizeof(m) / sizeof(m[0]));
+
+    if(result != JNI_OK){
+        ALOG("注册方法失败");
+        return JNI_VERSION_1_2;
+    }
+
+    //JNI_OnLoad需要一个int的返回值。
+    return JNI_VERSION_1_6;
+}
+
+```
+
+```
+C
+
+JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *reserved)
+{
+    (void)reserved;
+
+    if(NULL == vm) return JNI_ERR;
+    ////保存vm
+    kJvm = vm;
+
+    /// 动态注册Native方法
+    JNIEnv *env;
+    if(JNI_OK != (*vm)->GetEnv(vm, (void **)&env, HACKER_JNI_VERSION)) return JNI_ERR;
+    if(NULL == env || NULL == *env) return JNI_ERR;
+
+    jclass cls;
+    if(NULL == (cls = (*env)->FindClass(env, HOOK_JNI_CLASS_NAME))) return JNI_ERR;
+
+    JNINativeMethod m[] = {
+            {"nativeHook", "(I)I", (void *)hacker_hook},
+            {"nativeUnhook", "()I", (void *)hacker_unhook},
+            {"nativeThreadHook", "()V", (void *)enableThreadHook},
+    };
+    if(0 != (*env)->RegisterNatives(env, cls, m, sizeof(m) / sizeof(m[0]))) return JNI_ERR;
+
+    return HACKER_JNI_VERSION;
+}
+```
+
+### 静态注册
+
+方法名关联Java类路径。如Java_com_jni_senthinkprivate_MainActivity_stringFromJNI
+
+## 打包SO库
+
+/app/build.gradle下选择需要编译的平台架构
+
+```
+ externalNativeBuild {
+            cmake {
+                cppFlags ''
+                abiFilters "armeabi-v7a","arm64-v8a","x86"
+            }
+        }
+```
+
+## 项目依赖
+
+### cpp目录下多个文件夹编译
+
+- 工程目录如：
+
+```
+--- cpp
+  --	hook
+  	--CMakeLists.txt
+  	-- hook.cpp
+  -- CMakeLists.txt
+  -- test.cpp
+```
+
+-  首先在各文件目录下新增CMakeLists.txt配置文件：
+
+```
+cmake_minimum_required(VERSION 3.10.2)
+set(UTILS_SOURCE
+        threadLinker.cpp
+
+        )
+add_library(hook
+        SHARED
+        ${UTILS_SOURCE}
+
+        )
+target_link_libraries(hook)
+```
+
+- 在/cpp目录下的CMakeLists.txt中加入subDirectory，设置 target 需要链接的库：
+
+```
+add_subdirectory(hook)
+include_directories(hook)
+...
+target_link_libraries( # Specifies the target library.
+                       native-lib
+                       hook
+
+                       # Links the target library to the log library
+                       # included in the NDK.
+                       ${log-lib} )
+```
+
+- Cmake有关释义详见[链接](https://blog.csdn.net/afei__/article/details/81201039)
+
+