/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "ape/lib/pc.h"
#include "libc/assert.h"

static textreal uint64_t __pushpagetable(uint64_t *ptsp) {
  return (*ptsp -= PAGESIZE) | PAGE_V | PAGE_RW;
}

textreal uint64_t *__getpagetableentry(int64_t vaddr, unsigned depth,
                                       struct PageTable *pml4t,
                                       uint64_t *ptsp) {
  uint64_t *entry;
  unsigned char shift;
  assert(depth <= 3);
  assert(!(*ptsp & 0xfff));
  assert(!((uintptr_t)pml4t & 0xfff));
  shift = 39;
  for (;;) {
    entry = &pml4t->p[(vaddr >> shift) & 511];
    if (!depth--) return entry;
    shift -= 9;
    if (!*entry) *entry = __pushpagetable(ptsp);
    pml4t = (void *)(*entry & PAGE_TA);
  }
}