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
42static 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 */
62void 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}
80