问题描述

how current marco works in IA32

When I brose the code in Linux kernel 2.6.24, I find this.

 static __always_inline struct task_struct *get_current(void)
{
        return x86_read_percpu(current_task);
}

When I am looking for x86_read_percpue, It looks like this.

 #define x86_read_percpu(var) percpu_from_op("mov", per_cpu__##var)

But it seems like this.

 #define percpu_from_op(op,var)
        ({
                typeof(var) ret__;
                switch (sizeof(var)) {
                case 1:
                        asm(op "b "__percpu_seg"%1,%0"
                            : "=r" (ret__)
                            : "m" (var));
                        break;
                case 2:
                        asm(op "w "__percpu_seg"%1,%0"
                            : "=r" (ret__)
                            : "m" (var));
                        break;
                case 4:
                        asm(op "l "__percpu_seg"%1,%0"
                            : "=r" (ret__)
                            : "m" (var));
                        break;
                default: __bad_percpu_size();
                }
                ret__; })

I can't find per_cpu_current_task in source code!!!!!!!

解决方案

This had me beating my head against the wall for days. Now as you know, It is fairly straightforward to open an SDL surface in a window:
SDL_Surface *screen = SDL_SetVideoMode(width, height, 24, SDL_......
答案就在这里：How to make an SDL window the child of another window in Win32