arch/x86_64/mm/mmap.c

   1 /* Copyright 2005 Andi Kleen, SuSE Labs.
   2  * Licensed under GPL, v.2
   3  */
   4 #include <linux/config.h>
   5 #include <linux/mm.h>
   6 #include <linux/sched.h>
   7 #include <linux/random.h>
   8 #include <asm/ia32.h>
   9
  10 /* Notebook: move the mmap code from sys_x86_64.c over here. */
  11
  12 void arch_pick_mmap_layout(struct mm_struct *mm)
  13 {
  14 #ifdef CONFIG_IA32_EMULATION
  15         if (current_thread_info()->flags & _TIF_IA32)
  16                 return ia32_pick_mmap_layout(mm);
  17 #endif
  18         mm->mmap_base = TASK_UNMAPPED_BASE;
  19         if (current->flags & PF_RANDOMIZE) {
  20                 /* Add 28bit randomness which is about 40bits of address space
  21                    because mmap base has to be page aligned.
  22                    or ~1/128 of the total user VM
  23                    (total user address space is 47bits) */
  24                 unsigned rnd = get_random_int() & 0xfffffff;
  25                 mm->mmap_base += ((unsigned long)rnd) << PAGE_SHIFT;
  26         }
  27         mm->get_unmapped_area = arch_get_unmapped_area;
  28         mm->unmap_area = arch_unmap_area;
  29 }
  30