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

我有一个已实现的共享库，并希望 .so 调用在加载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);

共享库如何调用inmain_function，而不管inmain_function 是在主程序中定义的.

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 调用 main.c 中的符号，反之亦然，这是常见的用法.

推荐答案

您需要在 .so 中创建一个 register 函数，以便可执行文件可以为您的 .so 提供一个函数指针，以备后用.

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.

像这样:

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 中的一个变量中，以便 .so 中的其他函数可以找到它.

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.

你的 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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