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mp6sgfx3h 2 years ago
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fork.c
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/*
* linux/kernel/fork.c
*
* (C) 1991 Linus Torvalds
*/
/*
* 'fork.c' contains the help-routines for the 'fork' system call
* (see also system_call.s), and some misc functions ('verify_area').
* Fork is rather simple, once you get the hang of it, but the memory
* management can be a bitch. See 'mm/mm.c': 'copy_page_tables()'
*/
#include <errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <asm/segment.h>
#include <asm/system.h>
extern void write_verify(unsigned long address);
long last_pid=0;
void verify_area(void * addr,int size)
{
unsigned long start;
start = (unsigned long) addr;
size += start & 0xfff;
start &= 0xfffff000;
start += get_base(current->ldt[2]);
while (size>0) {
size -= 4096;
write_verify(start);
start += 4096;
}
}
int copy_mem(int nr,struct task_struct * p,int flag)
{
unsigned long old_data_base,new_data_base,data_limit;
unsigned long old_code_base,new_code_base,code_limit;
code_limit=get_limit(0x0f);
data_limit=get_limit(0x17);
old_code_base = get_base(current->ldt[1]);
old_data_base = get_base(current->ldt[2]);
if (old_data_base != old_code_base)
panic("We don't support separate I&D");
if (data_limit < code_limit)
panic("Bad data_limit");
new_data_base = new_code_base = nr * 0x4000000;
p->start_code = new_code_base;
set_base(p->ldt[1],new_code_base);
set_base(p->ldt[2],new_data_base);
if (copy_page_tables(old_data_base,new_data_base,data_limit,flag)) {
free_page_tables(new_data_base,data_limit);
return -ENOMEM;
}
return 0;
}
/*
* Ok, this is the main fork-routine. It copies the system process
* information (task[nr]) and sets up the necessary registers. It
* also copies the data segment in it's entirety.
*/
int copy_process(int flag,int nr,long ebp,long edi,long esi,long gs,long none,
long ebx,long ecx,long edx,
long fs,long es,long ds,
long eip,long cs,long eflags,long esp,long ss)
{
struct task_struct *p;
int i;
struct file *f;
p = (struct task_struct *) get_free_page();
if (!p)
return -EAGAIN;
task[nr] = p;
__asm__ volatile ("cld"); /* by wyj */
*p = *current; /* NOTE! this doesn't copy the supervisor stack */
p->state = TASK_UNINTERRUPTIBLE;
p->pid = last_pid;
p->father = current->pid;
p->counter = p->priority;
p->signal = 0;
p->alarm = 0;
p->leader = 0; /* process leadership doesn't inherit */
p->utime = p->stime = 0;
p->cutime = p->cstime = 0;
p->start_time = jiffies;
p->tss.back_link = 0;
p->tss.esp0 = PAGE_SIZE + (long) p;
p->tss.ss0 = 0x10;
p->tss.eip = eip;
p->tss.eflags = eflags;
p->tss.eax = 0;
p->tss.ecx = ecx;
p->tss.edx = edx;
p->tss.ebx = ebx;
p->tss.esp = esp;
p->tss.ebp = ebp;
p->tss.esi = esi;
p->tss.edi = edi;
p->tss.es = es & 0xffff;
p->tss.cs = cs & 0xffff;
p->tss.ss = ss & 0xffff;
p->tss.ds = ds & 0xffff;
p->tss.fs = fs & 0xffff;
p->tss.gs = gs & 0xffff;
p->tss.ldt = _LDT(nr);
p->tss.trace_bitmap = 0x80000000;
if (last_task_used_math == current)
__asm__("clts ; fnsave %0"::"m" (p->tss.i387));
if (copy_mem(nr,p,flag)) {
task[nr] = NULL;
free_page((long) p);
return -EAGAIN;
}
for (i=0; i<NR_OPEN;i++)
if (f=p->filp[i])
f->f_count++;
if (current->pwd)
current->pwd->i_count++;
if (current->root)
current->root->i_count++;
if (current->executable)
current->executable->i_count++;
set_tss_desc(gdt+(nr<<1)+FIRST_TSS_ENTRY,&(p->tss));
set_ldt_desc(gdt+(nr<<1)+FIRST_LDT_ENTRY,&(p->ldt));
p->state = TASK_RUNNING; /* do this last, just in case */
return last_pid;
}
int find_empty_process(void)
{
int i;
repeat:
if ((++last_pid)<0) last_pid=1;
for(i=0 ; i<NR_TASKS ; i++)
if (task[i] && task[i]->pid == last_pid) goto repeat;
for(i=1 ; i<NR_TASKS ; i++)
if (!task[i])
return i;
return -EAGAIN;
}
/*
直接让esp（子进程）指向另一个进程（当前进程）的地址；
修改eip对应的指令，改为ret 0xec8353c3 ps:应该只有0xc3有用
由于eip只执行一条指令，我们将eip指向栈，将ret压入栈即可；
在这里我们只实现了int (*fn)(void *) 一种函数类型，并且要求fn内以exit结尾
于是我们只需修改八字节即可；
下面写的不对，不能指向另一个进程的地址，只能修改物理页了。
*/
int do_clone(int nr,long tmp,int (*fn)(void *), void *child_stack, int flag)
{
//设置压栈表，方便操作；
long stack[1024];
unsigned long len=0;
task[nr]->tss.esp=(unsigned long) child_stack - 8;
stack[0] = (unsigned long) fn;
task[nr]->tss.eip = (unsigned long) child_stack - 4;
stack[1]= 0xec8353c3;
//栈区赋值；
len = 8;
char *p1=stack ,*p2=(char *)((unsigned long)child_stack-len);
while(len--)
put_fs_byte(*(p1++),p2++);
return 0;
}
/*
共享物理页：写法有缺陷，可能child——stack跨页
//子进程task[nr]的页表项获取，目的是更新成child——stacK的物理页
nrfrom_page = ((address>>20) & 0xffc);
nrfrom_page += ((task[nr]->start_code>>20) & 0xffc);//页目录
nrfrom=*(unsigned long *)nrfrom_page; //页表项
if(!(nrfrom&1)) //无页表项分配一个
{
if(!(tpage=get_free_page()))
{
printk("out of memory.\n");
return -1;
}
else
{
*(unsigned long *)nrfrom_page= tpage | 7;
mem_map[(tpage-LOW_MEM)>>12]++;
}
}
nrfrom &= 0xfffff000;
nrfrom_page = nrfrom + ((address>>10) & 0xffc);
//获取child_stack的物理页,并将其复制给task[nr];
address=(unsigned long) child_stack;
from_page = ((address>>20) & 0xffc);
from_page += ((current->start_code>>20) & 0xffc);//页目录
if(!(*(unsigned long *)from_page&1)) //页表项不存在，申请页面
if(!(tpage=get_free_page()))
{
printk("out of memory.\n");
return -1;
}
else
{
*(unsigned long *)from_page= tpage | 7;
mem_map[(tpage-LOW_MEM)>>12]++;
}
from=*(unsigned long *)from_page; //页表项
from &= 0xfffff000;
from_page = from + ((address>>10) & 0xffc);
if(!(*(unsigned long *)from_page & 1)) //物理页不存在
if(!(tpage=get_free_page()))
{
printk("out of memory.\n");
return -1;
}
else
{
*(unsigned long *)from_page= tpage | 7;
mem_map[(tpage-LOW_MEM)>>12]++;
}
//复制给nr
*(unsigned long *)nrfrom_page = *(unsigned long *)from_page;
//更新esp,让其指向child_stack同样偏移的地点;
task[nr]->tss.esp=(unsigned long) child_stack;
//注意：这里child_stack 指向的是高地址，要向下面push.
unsigned long phy_addr = (*(unsigned long *)nrfrom_page & 0xfffff000) | ((unsigned long) child_stack & 0xfff);
if(argv)//参数列表不为空，将参数压入栈中，这里直接修改物理页
{
}
//char * tmp1=nrfrom, *tmp2=child_stack-1024,len=;
//while()
return 0;
}
*/
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