LXR linux/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#include <linux/sched.h>
  31
  32/*
  33 * Top of mmap area (just below the process stack).
  34 *
  35 * Leave an at least ~128 MB hole.
  36 */
  37#define MIN_GAP (128*1024*1024)
  38#define MAX_GAP (TASK_SIZE/6*5)
  39
  40static inline unsigned long mmap_base(struct mm_struct *mm)
  41{
  42        unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
  43        unsigned long random_factor = 0;
  44
  45        if (current->flags & PF_RANDOMIZE)
  46                random_factor = get_random_int() % (1024*1024);
  47
  48        if (gap < MIN_GAP)
  49                gap = MIN_GAP;
  50        else if (gap > MAX_GAP)
  51                gap = MAX_GAP;
  52
  53        return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
  54}
  55
  56/*
  57 * This function, called very early during the creation of a new
  58 * process VM image, sets up which VM layout function to use:
  59 */
  60void arch_pick_mmap_layout(struct mm_struct *mm)
  61{
  62        /*
  63         * Fall back to the standard layout if the personality
  64         * bit is set, or if the expected stack growth is unlimited:
  65         */
  66        if (sysctl_legacy_va_layout ||
  67                        (current->personality & ADDR_COMPAT_LAYOUT) ||
  68                        current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY) {
  69                mm->mmap_base = TASK_UNMAPPED_BASE;
  70                mm->get_unmapped_area = arch_get_unmapped_area;
  71                mm->unmap_area = arch_unmap_area;
  72        } else {
  73                mm->mmap_base = mmap_base(mm);
  74                mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  75                mm->unmap_area = arch_unmap_area_topdown;
  76        }
  77}
  78