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