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/sched.h>
  28
  29 /*
  30  * Top of mmap area (just below the process stack).
  31  *
  32  * Leave an at least ~128 MB hole.
  33  */
  34 #define MIN_GAP (128*1024*1024)
  35 #define MAX_GAP (TASK_SIZE/6*5)
  36
  37 static inline unsigned long mmap_base(void)
  38 {
  39         unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
  40
  41         if (gap < MIN_GAP)
  42                 gap = MIN_GAP;
  43         else if (gap > MAX_GAP)
  44                 gap = MAX_GAP;
  45
  46         return TASK_SIZE - (gap & PAGE_MASK);
  47 }
  48
  49 static inline int mmap_is_legacy(void)
  50 {
  51         /*
  52          * Force standard allocation for 64 bit programs.
  53          */
  54         if (!test_thread_flag(TIF_32BIT))
  55                 return 1;
  56
  57         if (current->personality & ADDR_COMPAT_LAYOUT)
  58                 return 1;
  59
  60         if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
  61                 return 1;
  62
  63         return sysctl_legacy_va_layout;
  64 }
  65
  66 /*
  67  * This function, called very early during the creation of a new
  68  * process VM image, sets up which VM layout function to use:
  69  */
  70 void arch_pick_mmap_layout(struct mm_struct *mm)
  71 {
  72         /*
  73          * Fall back to the standard layout if the personality
  74          * bit is set, or if the expected stack growth is unlimited:
  75          */
  76         if (mmap_is_legacy()) {
  77                 mm->mmap_base = TASK_UNMAPPED_BASE;
  78                 mm->get_unmapped_area = arch_get_unmapped_area;
  79                 mm->unmap_area = arch_unmap_area;
  80         } else {
  81                 mm->mmap_base = mmap_base();
  82                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  83                 mm->unmap_area = arch_unmap_area_topdown;
  84         }
  85 }