arch/x86/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 #include <linux/sched.h>
  33
  34 /*
  35  * Top of mmap area (just below the process stack).
  36  *
  37  * Leave an at least ~128 MB hole.
  38  */
  39 #define MIN_GAP (128*1024*1024)
  40 #define MAX_GAP (TASK_SIZE/6*5)
  41
  42 static inline unsigned long mmap_base(struct mm_struct *mm)
  43 {
  44         unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
  45         unsigned long random_factor = 0;
  46
  47         if (current->flags & PF_RANDOMIZE)
  48                 random_factor = get_random_int() % (1024*1024);
  49
  50         if (gap < MIN_GAP)
  51                 gap = MIN_GAP;
  52         else if (gap > MAX_GAP)
  53                 gap = MAX_GAP;
  54
  55         return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
  56 }
  57
  58 /*
  59  * This function, called very early during the creation of a new
  60  * process VM image, sets up which VM layout function to use:
  61  */
  62 void ia32_pick_mmap_layout(struct mm_struct *mm)
  63 {
  64         /*
  65          * Fall back to the standard layout if the personality
  66          * bit is set, or if the expected stack growth is unlimited:
  67          */
  68         if (sysctl_legacy_va_layout ||
  69                         (current->personality & ADDR_COMPAT_LAYOUT) ||
  70                         current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY) {
  71                 mm->mmap_base = TASK_UNMAPPED_BASE;
  72                 mm->get_unmapped_area = arch_get_unmapped_area;
  73                 mm->unmap_area = arch_unmap_area;
  74         } else {
  75                 mm->mmap_base = mmap_base(mm);
  76                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  77                 mm->unmap_area = arch_unmap_area_topdown;
  78         }
  79 }