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comparison libmudflap/mf-heuristics.c @ 0:a06113de4d67

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author kent <kent@cr.ie.u-ryukyu.ac.jp>
date Fri, 17 Jul 2009 14:47:48 +0900
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1 /* Mudflap: narrow-pointer bounds-checking by tree rewriting.
2 Copyright (C) 2002, 2003, 2009 Free Software Foundation, Inc.
3 Contributed by Frank Ch. Eigler <fche@redhat.com>
4 and Graydon Hoare <graydon@redhat.com>
5
6 This file is part of GCC.
7
8 GCC is free software; you can redistribute it and/or modify it under
9 the terms of the GNU General Public License as published by the Free
10 Software Foundation; either version 3, or (at your option) any later
11 version.
12
13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
15 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 for more details.
17
18 Under Section 7 of GPL version 3, you are granted additional
19 permissions described in the GCC Runtime Library Exception, version
20 3.1, as published by the Free Software Foundation.
21
22 You should have received a copy of the GNU General Public License and
23 a copy of the GCC Runtime Library Exception along with this program;
24 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
25 <http://www.gnu.org/licenses/>. */
26
27 #include "config.h"
28
29 #include <stdio.h>
30
31 #include "mf-runtime.h"
32 #include "mf-impl.h"
33
34 #ifdef _MUDFLAP
35 #error "Do not compile this file with -fmudflap!"
36 #endif
37
38
39 extern char _end[];
40 extern char ENTRY_POINT[];
41
42
43 /* Run some quick validation of the given region.
44 Return -1 / 0 / 1 if the access known-invalid, possibly-valid, or known-valid.
45 */
46 int
47 __mf_heuristic_check (uintptr_t ptr, uintptr_t ptr_high)
48 {
49 VERBOSE_TRACE ("mf: heuristic check\n");
50
51 /* XXX: Disable the stack bounding check for libmudflapth. We do
52 actually have enough information to track stack bounds (see
53 __mf_pthread_info in mf-hooks.c), so with a bit of future work,
54 this heuristic can be turned on. */
55 #ifndef LIBMUDFLAPTH
56
57 /* The first heuristic is to check stack bounds. This is a
58 transient condition and quick to check. */
59 if (__mf_opts.heur_stack_bound)
60 {
61 uintptr_t stack_top_guess = (uintptr_t)__builtin_frame_address(0);
62 #if defined(__i386__) && defined (__linux__)
63 uintptr_t stack_segment_base = 0xC0000000; /* XXX: Bad assumption. */
64 #else
65 /* Cause tests to fail. */
66 uintptr_t stack_segment_base = 0;
67 #endif
68
69 VERBOSE_TRACE ("mf: stack estimated as %p-%p\n",
70 (void *) stack_top_guess, (void *) stack_segment_base);
71
72 if (ptr_high <= stack_segment_base &&
73 ptr >= stack_top_guess &&
74 ptr_high >= ptr)
75 {
76 return 1;
77 }
78 }
79 #endif
80
81
82 /* The second heuristic is to scan the range of memory regions
83 listed in /proc/self/maps, a special file provided by the Linux
84 kernel. Its results may be cached, and in fact, a GUESS object
85 may as well be recorded for interesting matching sections. */
86 if (__mf_opts.heur_proc_map)
87 {
88 /* Keep a record of seen records from /proc/self/map. */
89 enum { max_entries = 500 };
90 struct proc_self_map_entry
91 {
92 uintptr_t low;
93 uintptr_t high;
94 };
95 static struct proc_self_map_entry entry [max_entries];
96 static unsigned entry_used [max_entries];
97
98 /* Look for a known proc_self_map entry that may cover this
99 region. If one exists, then this heuristic has already run,
100 and should not be run again. The check should be allowed to
101 fail. */
102 unsigned i;
103 unsigned deja_vu = 0;
104 for (i=0; i<max_entries; i++)
105 {
106 if (entry_used[i] &&
107 (entry[i].low <= ptr) &&
108 (entry[i].high >= ptr_high))
109 deja_vu = 1;
110 }
111
112 if (! deja_vu)
113 {
114 /* Time to run the heuristic. Rescan /proc/self/maps; update the
115 entry[] array; XXX: remove expired entries, add new ones.
116 XXX: Consider entries that have grown (e.g., stack). */
117 char buf[512];
118 char flags[4];
119 void *low, *high;
120 FILE *fp;
121
122 fp = fopen ("/proc/self/maps", "r");
123 if (fp)
124 {
125 while (fgets (buf, sizeof(buf), fp))
126 {
127 if (sscanf (buf, "%p-%p %4c", &low, &high, flags) == 3)
128 {
129 if ((uintptr_t) low <= ptr &&
130 (uintptr_t) high >= ptr_high)
131 {
132 for (i=0; i<max_entries; i++)
133 {
134 if (! entry_used[i])
135 {
136 entry[i].low = (uintptr_t) low;
137 entry[i].high = (uintptr_t) high;
138 entry_used[i] = 1;
139 break;
140 }
141 }
142
143 VERBOSE_TRACE ("mf: registering region #%d "
144 "%p-%p given %s",
145 i, (void *) low, (void *) high, buf);
146
147 __mfu_register ((void *) low, (size_t) (high-low),
148 __MF_TYPE_GUESS,
149 "/proc/self/maps segment");
150
151 return 0; /* undecided (tending to cachable) */
152 }
153 }
154 }
155 fclose (fp);
156 }
157 }
158 }
159
160
161 /* The third heuristic is to approve all accesses between _start (or its
162 equivalent for the given target) and _end, which should include all
163 text and initialized data. */
164 if (__mf_opts.heur_start_end)
165 if (ptr >= (uintptr_t) & ENTRY_POINT && ptr_high <= (uintptr_t) & _end)
166 return 1; /* uncacheable */
167
168 return 0; /* unknown */
169 }