LXR linux/arch/powerpc/mm/mmap.c

   1/*
   2 *  flexible mmap layout support
   3 *
   4 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
   5 * All Rights Reserved.
   6 *
   7 * This program is free software; you can redistribute it and/or modify
   8 * it under the terms of the GNU General Public License as published by
   9 * the Free Software Foundation; either version 2 of the License, or
  10 * (at your option) any later version.
  11 *
  12 * This program is distributed in the hope that it will be useful,
  13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 * GNU General Public License for more details.
  16 *
  17 * You should have received a copy of the GNU General Public License
  18 * along with this program; if not, write to the Free Software
  19 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  20 *
  21 *
  22 * Started by Ingo Molnar <mingo@elte.hu>
  23 */
  24
  25#include <linux/personality.h>
  26#include <linux/mm.h>
  27#include <linux/random.h>
  28#include <linux/sched.h>
  29
  30/*
  31 * Top of mmap area (just below the process stack).
  32 *
  33 * Leave at least a ~128 MB hole on 32bit applications.
  34 *
  35 * On 64bit applications we randomise the stack by 1GB so we need to
  36 * space our mmap start address by a further 1GB, otherwise there is a
  37 * chance the mmap area will end up closer to the stack than our ulimit
  38 * requires.
  39 */
  40#define MIN_GAP32 (128*1024*1024)
  41#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
  42#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
  43#define MAX_GAP (TASK_SIZE/6*5)
  44
  45static inline int mmap_is_legacy(void)
  46{
  47        if (current->personality & ADDR_COMPAT_LAYOUT)
  48                return 1;
  49
  50        if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  51                return 1;
  52
  53        return sysctl_legacy_va_layout;
  54}
  55
  56static unsigned long mmap_rnd(void)
  57{
  58        unsigned long rnd = 0;
  59
  60        if (current->flags & PF_RANDOMIZE) {
  61                /* 8MB for 32bit, 1GB for 64bit */
  62                if (is_32bit_task())
  63                        rnd = (long)(get_random_int() % (1<<(23-PAGE_SHIFT)));
  64                else
  65                        rnd = (long)(get_random_int() % (1<<(30-PAGE_SHIFT)));
  66        }
  67        return rnd << PAGE_SHIFT;
  68}
  69
  70static inline unsigned long mmap_base(void)
  71{
  72        unsigned long gap = rlimit(RLIMIT_STACK);
  73
  74        if (gap < MIN_GAP)
  75                gap = MIN_GAP;
  76        else if (gap > MAX_GAP)
  77                gap = MAX_GAP;
  78
  79        return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
  80}
  81
  82/*
  83 * This function, called very early during the creation of a new
  84 * process VM image, sets up which VM layout function to use:
  85 */
  86void arch_pick_mmap_layout(struct mm_struct *mm)
  87{
  88        /*
  89         * Fall back to the standard layout if the personality
  90         * bit is set, or if the expected stack growth is unlimited:
  91         */
  92        if (mmap_is_legacy()) {
  93                mm->mmap_base = TASK_UNMAPPED_BASE;
  94                mm->get_unmapped_area = arch_get_unmapped_area;
  95        } else {
  96                mm->mmap_base = mmap_base();
  97                mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  98        }
  99}
 100