目录

hook

hook是什么

dlsym()函数

hook的实现步骤

加入hook的demo

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hook

hook可以把系统或第三方库提供的函数，替换成我们写的同名函数。会调用我们实现的函数。

hook是什么

hook提供了两个接口；1. dlsym()是针对系统的，系统原始的api。2. dlopen()是针对第三方的库。

dlsym()函数

获取共享对象或可执行文件中符号的地址。
函数原型：

描述：

        函数dlsym()接受dlopen()返回的动态加载共享对象的“句柄”以及以空结尾的符号名，并返回该符号加载到内存中的地址。如果在指定对象或加载对象时dlopen()自动加载的任何共享对象中找不到该符号，dlsym()将返回NULL。（dlsym()执行的搜索是通过这些共享对象的依赖关系树进行的广度优先搜索。）

        handle中可以指定两个特殊的伪句柄：

返回值：

成功时，这些函数返回与符号关联的地址。

失败时，返回NULL；可以使用dlerror()诊断错误的原因。

hook的实现步骤

/* ******* ******************hook****************** ******* */
//第一步定义目标函数一样的类型
typedef int (*pthread_mutex_lock_t)(pthread_mutex_t *mutex);
typedef int (*pthread_mutex_unlock_t)(pthread_mutex_t *mutex);pthread_mutex_lock_t pthread_mutex_lock_f;
pthread_mutex_unlock_t pthread_mutex_unlock_f;//第二步实现目标函数名一致
//pthread_mutex_lock()会调用本函数
int pthread_mutex_lock(pthread_mutex_t *mutex) {pthread_t selfid = pthread_self();pthread_mutex_lock_f(mutex);printf("pthread_mutex_lock: %ld, %p\n", selfid, mutex);
} //pthread_mutex_unlock()会调用本函数
int pthread_mutex_unlock(pthread_mutex_t *mutex) {pthread_t selfid = pthread_self();pthread_mutex_unlock_f(mutex);printf("pthread_mutex_unlock: %ld, %p\n", selfid, mutex);
} //第三步dlsym，放到main初始化
void init_hook(void) {pthread_mutex_lock_f = dlsym(RTLD_NEXT, "pthread_mutex_lock");pthread_mutex_unlock_f = dlsym(RTLD_NEXT, "pthread_mutex_unlock");
}

加入hook的demo

//gcc Dead_lock.c -lpthread -ldl
#define _GNU_SOURCE
#include <dlfcn.h>#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>#include <unistd.h>/* ******* ******************hook****************** ******* */
//第一步定义目标函数一样的类型
typedef int (*pthread_mutex_lock_t)(pthread_mutex_t *mutex);
typedef int (*pthread_mutex_unlock_t)(pthread_mutex_t *mutex);pthread_mutex_lock_t pthread_mutex_lock_f;
pthread_mutex_unlock_t pthread_mutex_unlock_f;//第二步实现目标函数名一致
//pthread_mutex_lock()会调用本函数
int pthread_mutex_lock(pthread_mutex_t *mutex) {pthread_t selfid = pthread_self();pthread_mutex_lock_f(mutex);printf("pthread_mutex_lock: %ld, %p\n", selfid, mutex);
} //pthread_mutex_unlock()会调用本函数
int pthread_mutex_unlock(pthread_mutex_t *mutex) {pthread_t selfid = pthread_self();pthread_mutex_unlock_f(mutex);printf("pthread_mutex_unlock: %ld, %p\n", selfid, mutex);
} //第三步dlsym，放到main初始化
void init_hook(void) {pthread_mutex_lock_f = dlsym(RTLD_NEXT, "pthread_mutex_lock");pthread_mutex_unlock_f = dlsym(RTLD_NEXT, "pthread_mutex_unlock");
}//测试代码
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex2 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex3 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex4 = PTHREAD_MUTEX_INITIALIZER;void *thread_funcA(void *arg) {pthread_mutex_lock(&mutex1);sleep(1);pthread_mutex_lock(&mutex2);printf("thread_funcA\n");pthread_mutex_unlock(&mutex2);pthread_mutex_unlock(&mutex1);}void *thread_funcB(void *arg) {pthread_mutex_lock(&mutex2);sleep(1);pthread_mutex_lock(&mutex3);printf("thread_funcB\n");pthread_mutex_unlock(&mutex3);pthread_mutex_unlock(&mutex2);}void *thread_funcC(void *arg) {pthread_mutex_lock(&mutex3);sleep(1);pthread_mutex_lock(&mutex4);printf("thread_funcC\n");pthread_mutex_unlock(&mutex4);pthread_mutex_unlock(&mutex3);
}void *thread_funcD(void *arg) {pthread_mutex_lock(&mutex4);sleep(1);pthread_mutex_lock(&mutex1);printf("thread_funcD\n");pthread_mutex_unlock(&mutex1);pthread_mutex_unlock(&mutex4);}int main() {pthread_t tida, tidb, tidc, tidd;init_hook();pthread_create(&tida, NULL, thread_funcA, NULL);pthread_create(&tidb, NULL, thread_funcB, NULL);pthread_create(&tidc, NULL, thread_funcC, NULL);pthread_create(&tidd, NULL, thread_funcD, NULL);pthread_join(tida, NULL);pthread_join(tidb, NULL);pthread_join(tidc, NULL);pthread_join(tidd, NULL);return 0;
}