arch/x86_64/ia32/mmap32.c

   1 /*
   2  *  linux/arch/x86_64/ia32/mm/mmap.c
   3  *
   4  *  flexible mmap layout support
   5  *
   6  * Based on the i386 version which was
   7  *
   8  * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
   9  * All Rights Reserved.
  10  *
  11  * This program is free software; you can redistribute it and/or modify
  12  * it under the terms of the GNU General Public License as published by
  13  * the Free Software Foundation; either version 2 of the License, or
  14  * (at your option) any later version.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  * GNU General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU General Public License
  22  * along with this program; if not, write to the Free Software
  23  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  24  *
  25  *
  26  * Started by Ingo Molnar <mingo@elte.hu>
  27  */
  28
  29 #include <linux/personality.h>
  30 #include <linux/mm.h>
  31 #include <linux/random.h>
  32
  33 /*
  34  * Top of mmap area (just below the process stack).
  35  *
  36  * Leave an at least ~128 MB hole.
  37  */
  38 #define MIN_GAP (128*1024*1024)
  39 #define MAX_GAP (TASK_SIZE/6*5)
  40
  41 static inline unsigned long mmap_base(struct mm_struct *mm)
  42 {
  43         unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
  44         unsigned long random_factor = 0;
  45
  46         if (current->flags & PF_RANDOMIZE)
  47                 random_factor = get_random_int() % (1024*1024);
  48
  49         if (gap < MIN_GAP)
  50                 gap = MIN_GAP;
  51         else if (gap > MAX_GAP)
  52                 gap = MAX_GAP;
  53
  54         return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
  55 }
  56
  57 /*
  58  * This function, called very early during the creation of a new
  59  * process VM image, sets up which VM layout function to use:
  60  */
  61 void ia32_pick_mmap_layout(struct mm_struct *mm)
  62 {
  63         /*
  64          * Fall back to the standard layout if the personality
  65          * bit is set, or if the expected stack growth is unlimited:
  66          */
  67         if (sysctl_legacy_va_layout ||
  68                         (current->personality & ADDR_COMPAT_LAYOUT) ||
  69                         current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY) {
  70                 mm->mmap_base = TASK_UNMAPPED_BASE;
  71                 mm->get_unmapped_area = arch_get_unmapped_area;
  72                 mm->unmap_area = arch_unmap_area;
  73         } else {
  74                 mm->mmap_base = mmap_base(mm);
  75                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  76                 mm->unmap_area = arch_unmap_area_topdown;
  77         }
  78 }