arch/i386/mm/mmap.c

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