共享库(.so)如何调用在其加载程序中实现的函数? [英] How can a shared library (.so) call a function that is implemented in its loading program?

问题描述

我有一个实现的共享库，并且希望.so调用在加载该库的主程序中实现的函数.

I have a shared library that I implemented and want the .so to call a function that's implemented in the main program which loads the library.

假设我有main.c(可执行文件)，其中包含:

Let's say I have main.c (executable) which contains:

void inmain_function(void*);
dlopen("libmy.so");

在my.c(libmy.so的代码)中，我想调用inmain_function:

In the my.c (the code for the libmy.so) I want to call inmain_function:

inmain_function(NULL);

无论事实是否在主程序中定义了inmain_function，共享库如何调用inmain_function.

How can the shared library call inmain_function regardless the fact inmain_function is defined in the main program.

注意:我想从my.c中调用main.c中的符号，而不是相反，这是常见用法.

推荐答案

您需要在.so中创建一个注册函数，以便可执行文件可以向.so提供函数指针，以供以后使用.

You'll need make a register function in your .so so that the executable can give a function pointer to your .so for it's later use.

赞:

void in_main_func () {
// this is the function that need to be called from a .so
}

void (*register_function)(void(*)());
void *handle = dlopen("libmylib.so");

register_function = dlsym(handle, "register_function");

register_function(in_main_func);

register_function需要将函数指针存储在.so中的变量中，.so中的其他函数才能找到它.

the register_function needs to store the function pointer in a variable in the .so where the other function in the .so can find it.

您的mylib.c需要看起来像这样:

Your mylib.c would the need to look something like this:

void (*callback)() = NULL;

void register_function( void (*in_main_func)())
{
    callback = in_main_func();
}

void function_needing_callback() 
{
     callback();
}

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