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 an at least ~128 MB hole.
35 #define MIN_GAP (128*1024*1024)
36 #define MAX_GAP (TASK_SIZE/6*5)
38 static inline int mmap_is_legacy(void)
40 if (current->personality & ADDR_COMPAT_LAYOUT)
43 if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
46 return sysctl_legacy_va_layout;
49 static unsigned long mmap_rnd(void)
51 unsigned long rnd = 0;
53 if (current->flags & PF_RANDOMIZE) {
54 /* 8MB for 32bit, 1GB for 64bit */
56 rnd = (long)(get_random_int() % (1<<(23-PAGE_SHIFT)));
58 rnd = (long)(get_random_int() % (1<<(30-PAGE_SHIFT)));
60 return rnd << PAGE_SHIFT;
63 static inline unsigned long mmap_base(void)
65 unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
69 else if (gap > MAX_GAP)
72 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
76 * This function, called very early during the creation of a new
77 * process VM image, sets up which VM layout function to use:
79 void arch_pick_mmap_layout(struct mm_struct *mm)
82 * Fall back to the standard layout if the personality
83 * bit is set, or if the expected stack growth is unlimited:
85 if (mmap_is_legacy()) {
86 mm->mmap_base = TASK_UNMAPPED_BASE;
87 mm->get_unmapped_area = arch_get_unmapped_area;
88 mm->unmap_area = arch_unmap_area;
90 mm->mmap_base = mmap_base();
91 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
92 mm->unmap_area = arch_unmap_area_topdown;