访问C ++类成员内联汇编 [英] Accessing C++ class member in inline assembly

问题描述

问：如何从非POD类中访问组件中的成员变量

Question: How can I access a member variable in assembly from within a non-POD class?

精化：

我已经写了一些内联汇编code一类的成员函数，但什么躲开我是如何访问类成员变量。我试着在 offsetof 宏观但这是一个非POD类。

I have written some inline assembly code for a class member function but what eludes me is how to access class member variables. I've tried the offsetof macro but this is a non-POD class.

我使用的是目前的解决方案是从全球范围内的指针分配给成员变量，但它是一个混乱的解决方案，我希望有更好的东西，我不知道。

The current solution I'm using is to assign a pointer from global scope to the member variable but it's a messy solution and I was hoping there was something better that I dont know about.

注意：我使用的是G ++编译器。与英特尔的语法ASM一个解决方案将是不错，但我会采取什么。

note: I'm using the G++ compiler. A solution with Intel syntax Asm would be nice but I'll take anything.

例如我想要做什么（Intel语法）：

example of what I want to do (intel syntax):

class SomeClass
{
  int* var_j;
  void set4(void)
  {
    asm("mov var_j, 4"); // sets pointer SomeClass::var_j to address "4"
  }
};

目前hackish的解决方案：

int* global_j;
class SomeClass
{
  int* var_j;
  void set4(void)
  {
    asm("mov global_j, 4"); // sets pointer global_j to address "4"
    var_j = global_j;       // copy it back to member variable :(
  }
};

这些都是原油的例子，但我认为他们得到跨越点。

Those are crude examples but I think they get the point across.

推荐答案

这是你所需要的：

__asm__ __volatile__ ("movl $4,%[v]" : [v] "+m" (var_j)) ;

编辑补充：汇编程序接受英特尔的语法，但是编译器不知道它，所以采用Intel语法这一招是不行的（不与G ++ 4.4.0，反正）

Edited to add: The assembler does accept Intel syntax, but the compiler doesn't know it, so this trick won't work using Intel syntax (not with g++ 4.4.0, anyway).

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