How to get the page directory of a pointer in xv6 - linux

Question

Here is my 'translate()' in proc.c
I want to get the physical address given the virtual address of a pointer, but I don't know how to get the pointers pgdir(page directory)...
int translate(void* vaddr)
{
cprintf("vaddr = %p\n",vaddr);
int paddr;
pde_t *pgdir;
pte_t *pgtab;
pde_t *pde;
pte_t *pte;
pgdir = (pde_t*)cpu->ts.cr3;
cprintf("page directory base is: %p\n",cpu->ts.cr3);
pde = &pgdir[PDX(vaddr)];
if(*pde & PTE_P){
pgtab = (pte_t*)P2V(PTE_ADDR(*pde));
}else{
cprintf("pde = %d\n",*pde);
cprintf("PTE_P = %d\n",PTE_P);
cprintf("pte not present\n");
return -1;
}
pte = &pgtab[PTX(vaddr)];
paddr = PTE_ADDR(*pte);
cprintf("the virtual address is %p\n",vaddr);
cprintf("the physical address is %d\n",paddr);
return 0;
}

Answer 1

You need to use argint() or argptr() to read the argument.

Answer 2

There's a global variable proc that lives in proc.h.
proc.h, lines 34 to 43
// Per-CPU variables, holding pointers to the
// current cpu and to the current process.
// The asm suffix tells gcc to use "%gs:0" to refer to cpu
// and "%gs:4" to refer to proc. seginit sets up the
// %gs segment register so that %gs refers to the memory
// holding those two variables in the local cpu's struct cpu.
// This is similar to how thread-local variables are implemented
// in thread libraries such as Linux pthreads.
extern struct cpu *cpu asm("%gs:0"); // &cpus[cpunum()]
extern struct proc *proc asm("%gs:4"); // cpus[cpunum()].proc
You can reference proc->pgdir in proc.c or anywhere else that proc.h is included.
For what it's worth your translate function looks good to me.