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1da177e4 LT |
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 | ||
31 | /* | |
32 | * Top of mmap area (just below the process stack). | |
33 | * | |
34 | * Leave an at least ~128 MB hole. | |
35 | */ | |
36 | #define MIN_GAP (128*1024*1024) | |
37 | #define MAX_GAP (TASK_SIZE/6*5) | |
38 | ||
39 | static inline unsigned long mmap_base(struct mm_struct *mm) | |
40 | { | |
41 | unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur; | |
42 | unsigned long random_factor = 0; | |
43 | ||
44 | if (current->flags & PF_RANDOMIZE) | |
45 | random_factor = get_random_int() % (1024*1024); | |
46 | ||
47 | if (gap < MIN_GAP) | |
48 | gap = MIN_GAP; | |
49 | else if (gap > MAX_GAP) | |
50 | gap = MAX_GAP; | |
51 | ||
52 | return PAGE_ALIGN(TASK_SIZE - gap - random_factor); | |
53 | } | |
54 | ||
55 | /* | |
56 | * This function, called very early during the creation of a new | |
57 | * process VM image, sets up which VM layout function to use: | |
58 | */ | |
59 | void arch_pick_mmap_layout(struct mm_struct *mm) | |
60 | { | |
61 | /* | |
62 | * Fall back to the standard layout if the personality | |
63 | * bit is set, or if the expected stack growth is unlimited: | |
64 | */ | |
65 | if (sysctl_legacy_va_layout || | |
66 | (current->personality & ADDR_COMPAT_LAYOUT) || | |
67 | current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY) { | |
68 | mm->mmap_base = TASK_UNMAPPED_BASE; | |
69 | mm->get_unmapped_area = arch_get_unmapped_area; | |
70 | mm->unmap_area = arch_unmap_area; | |
71 | } else { | |
72 | mm->mmap_base = mmap_base(mm); | |
73 | mm->get_unmapped_area = arch_get_unmapped_area_topdown; | |
74 | mm->unmap_area = arch_unmap_area_topdown; | |
75 | } | |
76 | } |