2 * flexible mmap layout support
4 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
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.
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.
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
22 * Started by Ingo Molnar <mingo@elte.hu>
25 #include <linux/personality.h>
27 #include <linux/random.h>
28 #include <linux/sched.h>
31 * Top of mmap area (just below the process stack).
33 * Leave at least a ~128 MB hole on 32bit applications.
35 * On 64bit applications we randomise the stack by 1GB so we need to
36 * space our mmap start address by a further 1GB, otherwise there is a
37 * chance the mmap area will end up closer to the stack than our ulimit
40 #define MIN_GAP32 (128*1024*1024)
41 #define MIN_GAP64 ((128 + 1024)*1024*1024UL)
42 #define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
43 #define MAX_GAP (TASK_SIZE/6*5)
45 static inline int mmap_is_legacy(void)
47 if (current
->personality
& ADDR_COMPAT_LAYOUT
)
50 if (rlimit(RLIMIT_STACK
) == RLIM_INFINITY
)
53 return sysctl_legacy_va_layout
;
56 static unsigned long mmap_rnd(void)
58 unsigned long rnd
= 0;
60 if (current
->flags
& PF_RANDOMIZE
) {
61 /* 8MB for 32bit, 1GB for 64bit */
63 rnd
= (long)(get_random_int() % (1<<(23-PAGE_SHIFT
)));
65 rnd
= (long)(get_random_int() % (1<<(30-PAGE_SHIFT
)));
67 return rnd
<< PAGE_SHIFT
;
70 static inline unsigned long mmap_base(void)
72 unsigned long gap
= rlimit(RLIMIT_STACK
);
76 else if (gap
> MAX_GAP
)
79 return PAGE_ALIGN(TASK_SIZE
- gap
- mmap_rnd());
83 * This function, called very early during the creation of a new
84 * process VM image, sets up which VM layout function to use:
86 void arch_pick_mmap_layout(struct mm_struct
*mm
)
89 * Fall back to the standard layout if the personality
90 * bit is set, or if the expected stack growth is unlimited:
92 if (mmap_is_legacy()) {
93 mm
->mmap_base
= TASK_UNMAPPED_BASE
;
94 mm
->get_unmapped_area
= arch_get_unmapped_area
;
96 mm
->mmap_base
= mmap_base();
97 mm
->get_unmapped_area
= arch_get_unmapped_area_topdown
;