text: #ifndef _ASM_X86_PAGE_64_DEFS_H
  #define _ASM_X86_PAGE_64_DEFS_H
  
  #define THREAD_SIZE_ORDER	1
  #define THREAD_SIZE  (PAGE_SIZE << THREAD_SIZE_ORDER)
  #define CURRENT_MASK (~(THREAD_SIZE - 1))
  
  #define EXCEPTION_STACK_ORDER 0
  #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
  
  #define DEBUG_STACK_ORDER (EXCEPTION_STACK_ORDER + 1)
  #define DEBUG_STKSZ (PAGE_SIZE << DEBUG_STACK_ORDER)
  
  #define IRQ_STACK_ORDER 2
  #define IRQ_STACK_SIZE (PAGE_SIZE << IRQ_STACK_ORDER)
  
  #define DOUBLEFAULT_STACK 1
  #define NMI_STACK 2
  #define DEBUG_STACK 3
  #define MCE_STACK 4
  #define N_EXCEPTION_STACKS 4  /* hw limit: 7 */
  
  #define PUD_PAGE_SIZE		(_AC(1, UL) << PUD_SHIFT)
  #define PUD_PAGE_MASK		(~(PUD_PAGE_SIZE-1))
  
  /*
   * Set __PAGE_OFFSET to the most negative possible address +
   * PGDIR_SIZE*16 (pgd slot 272).  The gap is to allow a space for a
   * hypervisor to fit.  Choosing 16 slots here is arbitrary, but it's
   * what Xen requires.
   */
  #define __PAGE_OFFSET           _AC(0xffff880000000000, UL)
  
  #define __START_KERNEL_map	_AC(0xffffffff80000000, UL)
  
  /* See Documentation/x86/x86_64/mm.txt for a description of the memory map. */
  #define __PHYSICAL_MASK_SHIFT	46
  #define __VIRTUAL_MASK_SHIFT	47
  
  /*
   * Kernel image size is limited to 512 MB (see level2_kernel_pgt in
   * arch/x86/kernel/head_64.S), and it is mapped here:
   */
  #define KERNEL_IMAGE_SIZE	(512 * 1024 * 1024)
  
  #endif /* _ASM_X86_PAGE_64_DEFS_H */
  