1 /* Mudflap: narrow-pointer bounds-checking by tree rewriting.
2 Copyright (C) 2002, 2003 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 2, or (at your option) any later
11 version.
12
13 In addition to the permissions in the GNU General Public License, the
14 Free Software Foundation gives you unlimited permission to link the
15 compiled version of this file into combinations with other programs,
16 and to distribute those combinations without any restriction coming
17 from the use of this file. (The General Public License restrictions
18 do apply in other respects; for example, they cover modification of
19 the file, and distribution when not linked into a combine
20 executable.)
21
22 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
23 WARRANTY; without even the implied warranty of MERCHANTABILITY or
24 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
25 for more details.
26
27 You should have received a copy of the GNU General Public License
28 along with GCC; see the file COPYING. If not, write to the Free
29 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
30 02110-1301, USA. */
31
32
33 #include "config.h"
34
35 #include <stdio.h>
36
37 #include "mf-runtime.h"
38 #include "mf-impl.h"
39
40 #ifdef _MUDFLAP
41 #error "Do not compile this file with -fmudflap!"
42 #endif
43
44
45 extern char _end[];
46 extern char ENTRY_POINT[];
47
48
49 /* Run some quick validation of the given region.
50 Return -1 / 0 / 1 if the access known-invalid, possibly-valid, or known-valid.
51 */
52 int
__mf_heuristic_check(uintptr_t ptr,uintptr_t ptr_high)53 __mf_heuristic_check (uintptr_t ptr, uintptr_t ptr_high)
54 {
55 VERBOSE_TRACE ("mf: heuristic check\n");
56
57 /* XXX: Disable the stack bounding check for libmudflapth. We do
58 actually have enough information to track stack bounds (see
59 __mf_pthread_info in mf-hooks.c), so with a bit of future work,
60 this heuristic can be turned on. */
61 #ifndef LIBMUDFLAPTH
62
63 /* The first heuristic is to check stack bounds. This is a
64 transient condition and quick to check. */
65 if (__mf_opts.heur_stack_bound)
66 {
67 uintptr_t stack_top_guess = (uintptr_t)__builtin_frame_address(0);
68 #if defined(__i386__) && defined (__linux__)
69 uintptr_t stack_segment_base = 0xC0000000; /* XXX: Bad assumption. */
70 #else
71 /* Cause tests to fail. */
72 uintptr_t stack_segment_base = 0;
73 #endif
74
75 VERBOSE_TRACE ("mf: stack estimated as %p-%p\n",
76 (void *) stack_top_guess, (void *) stack_segment_base);
77
78 if (ptr_high <= stack_segment_base &&
79 ptr >= stack_top_guess &&
80 ptr_high >= ptr)
81 {
82 return 1;
83 }
84 }
85 #endif
86
87
88 /* The second heuristic is to scan the range of memory regions
89 listed in /proc/self/maps, a special file provided by the Linux
90 kernel. Its results may be cached, and in fact, a GUESS object
91 may as well be recorded for interesting matching sections. */
92 if (__mf_opts.heur_proc_map)
93 {
94 /* Keep a record of seen records from /proc/self/map. */
95 enum { max_entries = 500 };
96 struct proc_self_map_entry
97 {
98 uintptr_t low;
99 uintptr_t high;
100 };
101 static struct proc_self_map_entry entry [max_entries];
102 static unsigned entry_used [max_entries];
103
104 /* Look for a known proc_self_map entry that may cover this
105 region. If one exists, then this heuristic has already run,
106 and should not be run again. The check should be allowed to
107 fail. */
108 unsigned i;
109 unsigned deja_vu = 0;
110 for (i=0; i<max_entries; i++)
111 {
112 if (entry_used[i] &&
113 (entry[i].low <= ptr) &&
114 (entry[i].high >= ptr_high))
115 deja_vu = 1;
116 }
117
118 if (! deja_vu)
119 {
120 /* Time to run the heuristic. Rescan /proc/self/maps; update the
121 entry[] array; XXX: remove expired entries, add new ones.
122 XXX: Consider entries that have grown (e.g., stack). */
123 char buf[512];
124 char flags[4];
125 void *low, *high;
126 FILE *fp;
127
128 fp = fopen ("/proc/self/maps", "r");
129 if (fp)
130 {
131 while (fgets (buf, sizeof(buf), fp))
132 {
133 if (sscanf (buf, "%p-%p %4c", &low, &high, flags) == 3)
134 {
135 if ((uintptr_t) low <= ptr &&
136 (uintptr_t) high >= ptr_high)
137 {
138 for (i=0; i<max_entries; i++)
139 {
140 if (! entry_used[i])
141 {
142 entry[i].low = (uintptr_t) low;
143 entry[i].high = (uintptr_t) high;
144 entry_used[i] = 1;
145 break;
146 }
147 }
148
149 VERBOSE_TRACE ("mf: registering region #%d "
150 "%p-%p given %s",
151 i, (void *) low, (void *) high, buf);
152
153 __mfu_register ((void *) low, (size_t) (high-low),
154 __MF_TYPE_GUESS,
155 "/proc/self/maps segment");
156
157 return 0; /* undecided (tending to cachable) */
158 }
159 }
160 }
161 fclose (fp);
162 }
163 }
164 }
165
166
167 /* The third heuristic is to approve all accesses between _start (or its
168 equivalent for the given target) and _end, which should include all
169 text and initialized data. */
170 if (__mf_opts.heur_start_end)
171 if (ptr >= (uintptr_t) & ENTRY_POINT && ptr_high <= (uintptr_t) & _end)
172 return 1; /* uncacheable */
173
174 return 0; /* unknown */
175 }
176