1 /* Linux host-specific hook definitions.
2 Copyright (C) 2004 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify it
7 under the terms of the GNU General Public License as published
8 by the Free Software Foundation; either version 2, or (at your
9 option) any later version.
11 GCC is distributed in the hope that it will be useful, but WITHOUT
12 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
13 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
14 License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING. If not, write to the
18 Free Software Foundation, 59 Temple Place - Suite 330, Boston,
19 MA 02111-1307, USA. */
23 #include "coretypes.h"
25 #include "hosthooks.h"
26 #include "hosthooks-def.h"
29 /* Linux has a feature called exec-shield-randomize that perturbs the
30 address of non-fixed mapped segments by a (relatively) small amount.
31 The feature is intended to make it harder to attack the system with
32 buffer overflow attacks, since every invocation of a program will
33 have its libraries and data segments at slightly different addresses.
35 This feature causes us problems with PCH because it makes it that
36 much harder to acquire a stable location at which to map our PCH
39 [ The feature causes other points of non-determinism within the
40 compiler as well, so we'd *really* like to be able to have the
41 driver disable exec-shield-randomize for the process group, but
42 that isn't possible at present. ]
44 We're going to try several things:
46 * Select an architecture specific address as "likely" and see
47 if that's free. For our 64-bit hosts, we can easily choose
48 an address in Never Never Land.
50 * If exec-shield-randomize is disabled, then just use the
51 address chosen by mmap in step one.
53 * If exec-shield-randomize is enabled, then temporarily allocate
54 32M of memory as a buffer, then allocate PCH memory, then
55 free the buffer. The theory here is that the perturbation is
56 no more than 16M, and so by allocating our buffer larger than
57 that we make it considerably more likely that the address will
58 be free when we want to load the data back.
61 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
62 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
64 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
65 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
67 /* For various ports, try to guess a fixed spot in the vm space
68 that's probably free. */
70 # define TRY_EMPTY_VM_SPACE 0x10000000000
72 # define TRY_EMPTY_VM_SPACE 0x2000000100000000
73 #elif defined(__x86_64)
74 # define TRY_EMPTY_VM_SPACE 0x1000000000
76 # define TRY_EMPTY_VM_SPACE 0x60000000
77 #elif defined(__powerpc__)
78 # define TRY_EMPTY_VM_SPACE 0x60000000
79 #elif defined(__s390x__)
80 # define TRY_EMPTY_VM_SPACE 0x8000000000
81 #elif defined(__s390__)
82 # define TRY_EMPTY_VM_SPACE 0x60000000
83 #elif defined(__sparc__) && defined(__LP64__)
84 # define TRY_EMPTY_VM_SPACE 0x8000000000
85 #elif defined(__sparc__)
86 # define TRY_EMPTY_VM_SPACE 0x60000000
88 # define TRY_EMPTY_VM_SPACE 0
91 /* Determine a location where we might be able to reliably allocate SIZE
92 bytes. FD is the PCH file, though we should return with the file
96 linux_gt_pch_get_address (size_t size
, int fd
)
98 size_t buffer_size
= 32 * 1024 * 1024;
103 addr
= mmap ((void *)TRY_EMPTY_VM_SPACE
, size
, PROT_READ
| PROT_WRITE
,
106 /* If we failed the map, that means there's *no* free space. */
107 if (addr
== (void *) MAP_FAILED
)
109 /* Unmap the area before returning. */
112 /* If we got the exact area we requested, then that's great. */
113 if (TRY_EMPTY_VM_SPACE
&& addr
== (void *) TRY_EMPTY_VM_SPACE
)
116 /* If we didn't, then we need to look to see if randomization is on. */
117 f
= fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
118 randomize_on
= false;
124 c
= fread (buf
, 1, sizeof buf
- 1, f
);
128 randomize_on
= (atoi (buf
) > 0);
133 /* If it isn't, then accept the address that mmap selected as fine. */
137 /* Otherwise, we need to try again with buffer space. */
138 buffer
= mmap (0, buffer_size
, PROT_NONE
, MAP_PRIVATE
| MAP_ANON
, -1, 0);
139 addr
= mmap (0, size
, PROT_READ
| PROT_WRITE
, MAP_PRIVATE
, fd
, 0);
140 if (buffer
!= (void *) MAP_FAILED
)
141 munmap (buffer
, buffer_size
);
142 if (addr
== (void *) MAP_FAILED
)
149 /* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at
150 mapping the data at BASE, -1 if we couldn't.
152 It's not possibly to reliably mmap a file using MAP_PRIVATE to
153 a specific START address on either hpux or linux. First we see
154 if mmap with MAP_PRIVATE works. If it does, we are off to the
155 races. If it doesn't, we try an anonymous private mmap since the
156 kernel is more likely to honor the BASE address in anonymous maps.
157 We then copy the data to the anonymous private map. This assumes
158 of course that we don't need to change the data in the PCH file
161 This approach obviously causes a performance penalty but there is
162 little else we can do given the current PCH implementation. */
165 linux_gt_pch_use_address (void *base
, size_t size
, int fd
, size_t offset
)
169 /* We're called with size == 0 if we're not planning to load a PCH
170 file at all. This allows the hook to free any static space that
171 we might have allocated at link time. */
175 /* Try to map the file with MAP_PRIVATE. */
176 addr
= mmap (base
, size
, PROT_READ
| PROT_WRITE
, MAP_PRIVATE
, fd
, offset
);
181 if (addr
!= (void *) MAP_FAILED
)
184 /* Try to make an anonymous private mmap at the desired location. */
185 addr
= mmap (base
, size
, PROT_READ
| PROT_WRITE
,
186 MAP_PRIVATE
| MAP_ANONYMOUS
, -1, 0);
190 if (addr
!= (void *) MAP_FAILED
)
195 if (lseek (fd
, offset
, SEEK_SET
) == (off_t
)-1)
202 nbytes
= read (fd
, base
, MIN (size
, SSIZE_MAX
));
205 base
= (char *) base
+ nbytes
;
213 const struct host_hooks host_hooks
= HOST_HOOKS_INITIALIZER
;