1 /*
2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
3  *
4  *   This program is free software; you can redistribute it and/or
5  *   modify it under the terms of the GNU General Public License
6  *   as published by the Free Software Foundation, version 2.
7  *
8  *   This program is distributed in the hope that it will be useful, but
9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
11  *   NON INFRINGEMENT.  See the GNU General Public License for
12  *   more details.
13  *
14  * Taken from the i386 architecture and simplified.
15  */
16 
17 #include <linux/mm.h>
18 #include <linux/random.h>
19 #include <linux/limits.h>
20 #include <linux/sched.h>
21 #include <linux/mman.h>
22 #include <linux/compat.h>
23 
24 /*
25  * Top of mmap area (just below the process stack).
26  *
27  * Leave an at least ~128 MB hole.
28  */
29 #define MIN_GAP (128*1024*1024)
30 #define MAX_GAP (TASK_SIZE/6*5)
31 
mmap_base(struct mm_struct * mm)32 static inline unsigned long mmap_base(struct mm_struct *mm)
33 {
34 	unsigned long gap = rlimit(RLIMIT_STACK);
35 	unsigned long random_factor = 0;
36 
37 	if (current->flags & PF_RANDOMIZE)
38 		random_factor = get_random_int() % (1024*1024);
39 
40 	if (gap < MIN_GAP)
41 		gap = MIN_GAP;
42 	else if (gap > MAX_GAP)
43 		gap = MAX_GAP;
44 
45 	return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
46 }
47 
48 /*
49  * This function, called very early during the creation of a new
50  * process VM image, sets up which VM layout function to use:
51  */
arch_pick_mmap_layout(struct mm_struct * mm)52 void arch_pick_mmap_layout(struct mm_struct *mm)
53 {
54 #if !defined(__tilegx__)
55 	int is_32bit = 1;
56 #elif defined(CONFIG_COMPAT)
57 	int is_32bit = is_compat_task();
58 #else
59 	int is_32bit = 0;
60 #endif
61 
62 	/*
63 	 * Use standard layout if the expected stack growth is unlimited
64 	 * or we are running native 64 bits.
65 	 */
66 	if (!is_32bit || rlimit(RLIMIT_STACK) == RLIM_INFINITY) {
67 		mm->mmap_base = TASK_UNMAPPED_BASE;
68 		mm->get_unmapped_area = arch_get_unmapped_area;
69 		mm->unmap_area = arch_unmap_area;
70 	} else {
71 		mm->mmap_base = mmap_base(mm);
72 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
73 		mm->unmap_area = arch_unmap_area_topdown;
74 	}
75 }
76