每个页的大小: 2^12 = 4096 Bytes
每个地址的大小: 8 Bytes
每个页能容纳:2^9 = 512 个地址
需要一个 9bit 的字段来索引映射表
一般来说,如果页面大小为 2^k,那么一个页面可以容纳 k-3 个指针
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/mm_types.h>
#include <linux/sched.h>
#include <linux/export.h>
static unsigned long cr0;
static unsigned long cr3;
static unsigned long vaddr = 0;
static void get_pgtable_macro(void)
{
cr0 = read_cr0();
cr3 = read_cr3_pa();
printk("cr0 = 0x%lx, cr3 = 0x%lx
", cr0, cr3);
printk("PGDIR_SHIFT = %d
", PGDIR_SHIFT);
printk("P4D_SHIFT = %d
", P4D_SHIFT);
printk("PUD_SHIFT = %d
", PUD_SHIFT);
printk("PMD_SHIFT = %d
", PMD_SHIFT);
printk("PAGE_SHIFT = %d
", PAGE_SHIFT);
//页目录表中项的个数
printk("PTRS_PER_PGD = %d
", PTRS_PER_PGD);
printk("PTRS_PER_P4D = %d
", PTRS_PER_P4D);
printk("PTRS_PER_PUD = %d
", PTRS_PER_PUD);
printk("PTRS_PER_PMD = %d
", PTRS_PER_PMD);
printk("PTRS_PER_PTE = %d
", PTRS_PER_PTE);
//页内偏移掩码,用来屏蔽 page_offset
printk("PAGEMASK = 0x%lx
", PAGE_MASK);
}
void vaddr2paddr(unsigned long vaddr)
{
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
unsigned long paddr = 0;
unsigned long page_addr = 0;
unsigned long page_offset = 0;
//取得页全局目录项
pgd = pgd_offset(current->mm, vaddr);
printk("pgd_val = 0x%lx, pgd_index = %lu
", pgd_val(*pgd), pgd_index(vaddr));
//取得 p4d
p4d = p4d_offset(pgd, vaddr);
printk("p4d_val = 0x%lx, p4d_index = %lu
", p4d_val(*p4d), p4d_index(vaddr));
//取得页上级目录项
pud = pud_offset(p4d, vaddr);
printk("pud_val = 0x%lx, pud_index = %lu
", pud_val(*pud), pud_index(vaddr));
//取得页中间目录项
pmd = pmd_offset(pud, vaddr);
printk("pmd_val = 0x%lx, pmd_index = %lu
", pmd_val(*pmd), pmd_index(vaddr));
//取得页表(在主内核页表中查找)
pte = pte_offset_kernel(pmd, vaddr);
printk("pte_val = 0x%lx, pte_index = %lu
", pte_val(*pte), pte_index(vaddr));
//取得的页表项的低 12 位放的是页属性
//所以用 PAGE_MASK 来清除
page_addr = pte_val(*pte) & PAGE_MASK;
//取得页内偏移 page_offset
//也就是只取虚拟地址的地 12 位
page_offset = vaddr & ~PAGE_MASK;
//然后和并页表地址和页内偏移取得物理地址
paddr = page_addr | page_offset;
printk("page_addr = 0x%lx, page_offset = 0x%lx
", page_addr, page_offset);
printk("virtual address = 0x%lx, physical address = 0x%lx
", vaddr, paddr);
}
static int __init v2p_init(void)
{
unsigned long vaddr = 0;
printk("vritual address to physical address module is running..
");
get_pgtable_macro();
printk("
");
vaddr = __get_free_page(GFP_KERNEL);
if(vaddr == 0)
{
printk("__get_free_page failed..
");
return 0;
}
printk("get_page_vaddr = 0x%lx
", vaddr);
vaddr2paddr(vaddr);
return 0;
}
static void __exit v2p_exit(void)
{
free_page(vaddr);
printk("module is leaving...
");
}
module_init(v2p_init);
module_exit(v2p_exit);