如何从动态负载库执行未知功能？ [英] How to execute unknown functions from dynamic load libraries?

问题描述

在设计时就知道从动态库中加载函数很容易。
只是这样做：

It's easy to load functions from dynamic libraries when you know this function in design time. just do something like this:

   int (*fn)(int);

   l0 = dlopen("./libfoo.so", RTLD_LAZY);
   if (!l0) 
   {
      fprintf(stderr, "l0 %s\n", dlerror());
      return 1;
   }


   fn = (int (*)(int))dlsym(l0, "foo");


   if ((error = dlerror()) != NULL)  
   {
      fprintf(stderr, "fn:%s\n", error);
      return 1;
   }

   x=(*fn)(y);

...

如何执行设计时未知的库函数？在运行时，您具有函数名称以及参数指针数组和参数大小数组：

How to execute library function when it's unknown in design time? In runtime you have a function name and array of arguments pointers and array of arguments sizes:

char * fn_name = foo;
int foo_argc;
void * foo_argv [];
int foo_argv_size [];

char* fn_name="foo"; int foo_argc; void* foo_argv[]; int foo_argv_size[];

在脚本语言中这是小菜一碟，但是如何在c ++中很好地实现呢？

In scripting language it's a piece a cake task, but how to implement this nicely in c++?

推荐答案

实际上，如果您知道函数的调用约定及其接收的参数，则实际上存在一种在运行时调用函数的方法。但这不属于标准的C / C ++语言范围。

There's actually a method to call a function at run-time if you know its calling convention and which parameters it receives. This however lies out of the standard C/C++ language scope.

对于x86汇编程序：

假设以下内容：

1. 您知道要在固态缓冲区中为函数准备所有参数，完全按照将其打包在堆栈中的方式


2. 您的函数不会按值获取/返回C ++对象。

您可以然后使用以下函数：

You may use then the following function:

int CallAnyFunc(PVOID pfn, PVOID pParams, size_t nSizeParams)
{
    // Reserve the space on the stack
    // This is equivalent (in some sense) to 'push' all the parameters into the stack.
    // NOTE: Don't just subtract the stack pointer, better to call _alloca, because it also takes
    // care of ensuring all the consumed memory pages are accessible
    _alloca(nSizeParams);

    // Obtain the stack top pointer
    char* pStack;
    _asm {
        mov pStack, esp
    };

    // Copy all the parameters into the stack
    // NOTE: Don't use the memcpy function. Because the call to it
    // will overwrite the stack (which we're currently building)
    for (size_t i = 0; i < nSizeParams; i++)
        pStack[i] = ((char*) pParams)[i];

    // Call your function
    int retVal;
    _asm {
        call pfn
        // Most of the calling conventions return the value of the function (if anything is returned)
        // in EAX register
        mov retVal, eax
    };

    return retVal;
}

您可能需要根据使用的调用约定调整此功能

You may need to adjust this function, depending on the calling convention used

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