2 * linux/arch/x86-64/mm/mmap.c
4 * flexible mmap layout support
6 * Based on code by Ingo Molnar and Andi Kleen, copyrighted
9 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
10 * All Rights Reserved.
11 * Copyright 2005 Andi Kleen, SUSE Labs.
12 * Copyright 2007 Jiri Kosina, SUSE Labs.
14 * This program is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU General Public License as published by
16 * the Free Software Foundation; either version 2 of the License, or
17 * (at your option) any later version.
19 * This program is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 * GNU General Public License for more details.
24 * You should have received a copy of the GNU General Public License
25 * along with this program; if not, write to the Free Software
26 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
30 #include <linux/personality.h>
32 #include <linux/random.h>
33 #include <linux/limits.h>
34 #include <linux/sched.h>
38 * Top of mmap area (just below the process stack).
40 * Leave an at least ~128 MB hole.
42 #define MIN_GAP (128*1024*1024)
43 #define MAX_GAP (TASK_SIZE/6*5)
45 static inline unsigned long mmap_base(void)
47 unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
51 else if (gap > MAX_GAP)
54 return TASK_SIZE - (gap & PAGE_MASK);
57 static inline int mmap_is_32(void)
59 #ifdef CONFIG_IA32_EMULATION
60 if (test_thread_flag(TIF_IA32))
66 static inline int mmap_is_legacy(void)
68 if (current->personality & ADDR_COMPAT_LAYOUT)
71 if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
74 return sysctl_legacy_va_layout;
78 * This function, called very early during the creation of a new
79 * process VM image, sets up which VM layout function to use:
81 void arch_pick_mmap_layout(struct mm_struct *mm)
84 if (current->flags & PF_RANDOMIZE) {
86 * Add 28bit randomness which is about 40bits of address space
87 * because mmap base has to be page aligned.
88 * or ~1/128 of the total user VM
89 * (total user address space is 47bits)
91 rnd = get_random_int() & 0xfffffff;
95 * Fall back to the standard layout if the personality
96 * bit is set, or if the expected stack growth is unlimited:
99 #ifdef CONFIG_IA32_EMULATION
100 /* ia32_pick_mmap_layout has its own. */
101 return ia32_pick_mmap_layout(mm);
103 } else if(mmap_is_legacy()) {
104 mm->mmap_base = TASK_UNMAPPED_BASE;
105 mm->get_unmapped_area = arch_get_unmapped_area;
106 mm->unmap_area = arch_unmap_area;
108 mm->mmap_base = mmap_base();
109 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
110 mm->unmap_area = arch_unmap_area_topdown;
111 if (current->flags & PF_RANDOMIZE)
114 if (current->flags & PF_RANDOMIZE) {
115 mm->mmap_base += ((long)rnd) << PAGE_SHIFT;