linux操作系统学习实践 －－－system.h

/* system.h
 *I don't mean to write the whole OS kernel.I just want to put what I have
 *already learned into practice.But what will it be end up looking like.
 *I don't know.ALA I have some free time,I will write something.Just like
 *linus once said,"Just for fun".I don't care what this small ugly codes
 *will be capable of,or does it worth something.I just write it for fun,
 *and for practice.

 *         10 / 13 / 2010        liangtao
 *            E-mail:[e-mail]
 */

#ifndef _SYSTEM_H
#define _SYSTEM_H
#include
#ifndef __ASM__
#include

#define cli() asm("cli":::"memory");
#define sti() asm("sti":::"memory")


#define __SET_SEG(SEGMENT, val) \
        asm volatile("movw %0, %%" #SEGMENT " "::"r"(val):"memory")

#define set_fs(val)  __SET_SEG(fs, val)
#define set_gs(val)  __SET_SEG(gs, val)

#define move_to_user_mode() \
    asm volatile("movl    %%esp, %%eax\n\t"        \
                     "pushl  $0x33\n\t"        \
                     "pushl    %%eax\n\t"                \
                     "pushfl\n\t"                        \
                     "pushl    $0x2b\n\t"        \
                     "pushl    $1f\n"                    \
                     "iret\n"                            \
                     "1: movw $0x33, %%ax\n\t"\
                     "movw %%ax, %%ds\n\t"            \
                     "movw %%ax, %%fs\n\t"            \
                     "movw %%ax, %%gs\n":::"ax")




struct task_struct *__switch_to(struct task_struct *prev, struct task_struct *next);

/*
 * speaking of switch_to a a newly forked process.the next-regs.eip
 * should be "ret_from_fork".So, we push it's eip onto it's kernel
 * mode stack, then push the param that needed by __switch_to.
 * i don't know how to pass the param directly by registers.
 * once i get it,i will fix it.it's a little bit awkward.
 * so when in the func, add esp by 8,then return.this will
 * pop out the eip.So next stop the newly forked process will be
 * at is "ret_from_fork"
 * !!!this seems to be too much.as i always get a little confused...-_-
 */

/*
 * it seems that if we want to pass the param by the stack.
 * here just push two param onto the stack and jump to __switch_to()
 * won't work!!!haaa...there should be a return address on the stack
 * when __switch_to() excutes,at least the compiler thinks so.
 * so push whatever onto the stack.But must add esp by 4 when
 * return from the __switch_to().Don't ask me why...
 */
#define switch_to(prev,next) \
    asm volatile("movl    %%esp, %0\n\t" \
                     "movl    $1f, %1\n\t"  \
                     "movl    %2, %%esp\n\t" \
                     "pushl    %3\n\t"    \
                     "pushl    %%edx\n\t" \
                     "pushl  %%eax\n\t" \
                     "pushl $0\n\t" \
                     "jmp __switch_to\n" \
                     "1:" :"=m"(prev->regs.esp0), "=m"(prev->regs.eip) \
                     :"m"(next->regs.esp0), "m"(next->regs.eip),  \
                     "a"(prev), "d"(next))


static inline int in_user_mode(void)
{
    int cs;
    asm("movw %%cs, %0":"=m"(cs));
    if((cs & 3) == 3)
        return 1;
    else
        return 0;
}    

#endif

#endif