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coperating-systemriscvxv6

Is it possible to manually change page table's PTE value? (xv6, risc-v,c)

xv6 uses 3 level page table. The question is in pte value! I'm printing a pagetable. And I keep noticing that my output's page table address in the beginning (...87f49000) is different from the second line pte (...21fd1401). I thought they sould be the same. Some say it is normal to have different pte value because os scheduling differs as time changes.

Am I missing something so that my page table turn out to be ugly? I just want the first two page table pte to be the same!

I was expecting an output like this (pte values are the same):

enter image description here

This is my output: enter image description here

My code (It's not important.):

static int level = 0;
static int print_end = 0;
static uint64 vadd_lv0 = 0;
static uint64 vadd_lv1 = 0;
static uint64 vadd_lv2 = 0;
static pte_t pte = 0;

void vmprint(pagetable_t pagetable) {
  if (level == 0){
    printf("page table %p\n", pagetable);
    print_end = 0;
    pte = pagetable;
  }
  // iterate 512 PTEs
  for (uint64 i = 0; i < 512; i++) {    
    uint64 va = 0;
    switch(level){
      case 0:
        vadd_lv0 = i<<30;
        va = vadd_lv0;
        break;
      case 1:
        vadd_lv1 = i<<21;
        va = vadd_lv0+vadd_lv1;
        break;
      case 2:
        vadd_lv2 = i<<12;
        va = vadd_lv0+vadd_lv1+vadd_lv2;
        break;
    }
    pte_t t = pagetable[i];
    if (t & PTE_V) {
      uint64 pa = PTE2PA(t);
      if (level==0 && i==255)
        print_end = 1;
      if (level != 0 && !print_end){     
        printf("|");
      }else if (level!=0){
        printf(" ");
      }
      for (int j = 0; j < (level-1)*4+3; j++) printf(" ");

      printf("+-- %d: pte=%p va=%p pa=%p",i, t, va, pa);
      printf((t&PTE_V)?" V":"");
      printf((t&PTE_R)?" R":"");
      printf((t&PTE_W)?" W":"");
      printf((t&PTE_X)?" X":"");
      printf((t&PTE_U)?" U":"");
      printf((t&PTE_D)?" D":"");

      printf("\n");

      // PTE without any WRX bit set points to low-level page table
      if ((t & (PTE_W|PTE_R|PTE_X)) == 0){

        level++;
        vmprint((pagetable_t)pa);
        level--;
      }
    }
  }
}
Solution

  • Shouldn't print the address store by the pte, but to print out the address of pte.