1/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
2 Copyright (C) 1996-2017 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19#include <assert.h>
20#include <unistd.h>
21#include <ldsodefs.h>
22#include <sys/mman.h>
23#include <dl-cache.h>
24#include <dl-procinfo.h>
25#include <stdint.h>
26#include <_itoa.h>
27#include <dl-hwcaps.h>
28
29#ifndef _DL_PLATFORMS_COUNT
30# define _DL_PLATFORMS_COUNT 0
31#endif
32
33/* This is the starting address and the size of the mmap()ed file. */
34static struct cache_file *cache;
35static struct cache_file_new *cache_new;
36static size_t cachesize;
37
38/* 1 if cache_data + PTR points into the cache. */
39#define _dl_cache_verify_ptr(ptr) (ptr < cache_data_size)
40
41#define SEARCH_CACHE(cache) \
42/* We use binary search since the table is sorted in the cache file. \
43 The first matching entry in the table is returned. \
44 It is important to use the same algorithm as used while generating \
45 the cache file. */ \
46do \
47 { \
48 left = 0; \
49 right = cache->nlibs - 1; \
50 \
51 while (left <= right) \
52 { \
53 __typeof__ (cache->libs[0].key) key; \
54 \
55 middle = (left + right) / 2; \
56 \
57 key = cache->libs[middle].key; \
58 \
59 /* Make sure string table indices are not bogus before using \
60 them. */ \
61 if (! _dl_cache_verify_ptr (key)) \
62 { \
63 cmpres = 1; \
64 break; \
65 } \
66 \
67 /* Actually compare the entry with the key. */ \
68 cmpres = _dl_cache_libcmp (name, cache_data + key); \
69 if (__glibc_unlikely (cmpres == 0)) \
70 { \
71 /* Found it. LEFT now marks the last entry for which we \
72 know the name is correct. */ \
73 left = middle; \
74 \
75 /* There might be entries with this name before the one we \
76 found. So we have to find the beginning. */ \
77 while (middle > 0) \
78 { \
79 __typeof__ (cache->libs[0].key) key; \
80 \
81 key = cache->libs[middle - 1].key; \
82 /* Make sure string table indices are not bogus before \
83 using them. */ \
84 if (! _dl_cache_verify_ptr (key) \
85 /* Actually compare the entry. */ \
86 || _dl_cache_libcmp (name, cache_data + key) != 0) \
87 break; \
88 --middle; \
89 } \
90 \
91 do \
92 { \
93 int flags; \
94 __typeof__ (cache->libs[0]) *lib = &cache->libs[middle]; \
95 \
96 /* Only perform the name test if necessary. */ \
97 if (middle > left \
98 /* We haven't seen this string so far. Test whether the \
99 index is ok and whether the name matches. Otherwise \
100 we are done. */ \
101 && (! _dl_cache_verify_ptr (lib->key) \
102 || (_dl_cache_libcmp (name, cache_data + lib->key) \
103 != 0))) \
104 break; \
105 \
106 flags = lib->flags; \
107 if (_dl_cache_check_flags (flags) \
108 && _dl_cache_verify_ptr (lib->value)) \
109 { \
110 if (best == NULL || flags == GLRO(dl_correct_cache_id)) \
111 { \
112 HWCAP_CHECK; \
113 best = cache_data + lib->value; \
114 \
115 if (flags == GLRO(dl_correct_cache_id)) \
116 /* We've found an exact match for the shared \
117 object and no general `ELF' release. Stop \
118 searching. */ \
119 break; \
120 } \
121 } \
122 } \
123 while (++middle <= right); \
124 break; \
125 } \
126 \
127 if (cmpres < 0) \
128 left = middle + 1; \
129 else \
130 right = middle - 1; \
131 } \
132 } \
133while (0)
134
135
136int
137internal_function
138_dl_cache_libcmp (const char *p1, const char *p2)
139{
140 while (*p1 != '\0')
141 {
142 if (*p1 >= '0' && *p1 <= '9')
143 {
144 if (*p2 >= '0' && *p2 <= '9')
145 {
146 /* Must compare this numerically. */
147 int val1;
148 int val2;
149
150 val1 = *p1++ - '0';
151 val2 = *p2++ - '0';
152 while (*p1 >= '0' && *p1 <= '9')
153 val1 = val1 * 10 + *p1++ - '0';
154 while (*p2 >= '0' && *p2 <= '9')
155 val2 = val2 * 10 + *p2++ - '0';
156 if (val1 != val2)
157 return val1 - val2;
158 }
159 else
160 return 1;
161 }
162 else if (*p2 >= '0' && *p2 <= '9')
163 return -1;
164 else if (*p1 != *p2)
165 return *p1 - *p2;
166 else
167 {
168 ++p1;
169 ++p2;
170 }
171 }
172 return *p1 - *p2;
173}
174
175
176/* Look up NAME in ld.so.cache and return the file name stored there, or null
177 if none is found. The cache is loaded if it was not already. If loading
178 the cache previously failed there will be no more attempts to load it.
179 The caller is responsible for freeing the returned string. The ld.so.cache
180 may be unmapped at any time by a completing recursive dlopen and
181 this function must take care that it does not return references to
182 any data in the mapping. */
183char *
184internal_function
185_dl_load_cache_lookup (const char *name)
186{
187 int left, right, middle;
188 int cmpres;
189 const char *cache_data;
190 uint32_t cache_data_size;
191 const char *best;
192
193 /* Print a message if the loading of libs is traced. */
194 if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
195 _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
196
197 if (cache == NULL)
198 {
199 /* Read the contents of the file. */
200 void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
201 PROT_READ);
202
203 /* We can handle three different cache file formats here:
204 - the old libc5/glibc2.0/2.1 format
205 - the old format with the new format in it
206 - only the new format
207 The following checks if the cache contains any of these formats. */
208 if (file != MAP_FAILED && cachesize > sizeof *cache
209 && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0)
210 {
211 size_t offset;
212 /* Looks ok. */
213 cache = file;
214
215 /* Check for new version. */
216 offset = ALIGN_CACHE (sizeof (struct cache_file)
217 + cache->nlibs * sizeof (struct file_entry));
218
219 cache_new = (struct cache_file_new *) ((void *) cache + offset);
220 if (cachesize < (offset + sizeof (struct cache_file_new))
221 || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
222 sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
223 cache_new = (void *) -1;
224 }
225 else if (file != MAP_FAILED && cachesize > sizeof *cache_new
226 && memcmp (file, CACHEMAGIC_VERSION_NEW,
227 sizeof CACHEMAGIC_VERSION_NEW - 1) == 0)
228 {
229 cache_new = file;
230 cache = file;
231 }
232 else
233 {
234 if (file != MAP_FAILED)
235 __munmap (file, cachesize);
236 cache = (void *) -1;
237 }
238
239 assert (cache != NULL);
240 }
241
242 if (cache == (void *) -1)
243 /* Previously looked for the cache file and didn't find it. */
244 return NULL;
245
246 best = NULL;
247
248 if (cache_new != (void *) -1)
249 {
250 uint64_t platform;
251
252 /* This is where the strings start. */
253 cache_data = (const char *) cache_new;
254
255 /* Now we can compute how large the string table is. */
256 cache_data_size = (const char *) cache + cachesize - cache_data;
257
258 platform = _dl_string_platform (GLRO(dl_platform));
259 if (platform != (uint64_t) -1)
260 platform = 1ULL << platform;
261
262 uint64_t hwcap_mask = GET_HWCAP_MASK();
263
264#define _DL_HWCAP_TLS_MASK (1LL << 63)
265 uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & hwcap_mask)
266 | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
267
268 /* Only accept hwcap if it's for the right platform. */
269#define HWCAP_CHECK \
270 if (lib->hwcap & hwcap_exclude) \
271 continue; \
272 if (GLRO(dl_osversion) && lib->osversion > GLRO(dl_osversion)) \
273 continue; \
274 if (_DL_PLATFORMS_COUNT \
275 && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0 \
276 && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform) \
277 continue
278 SEARCH_CACHE (cache_new);
279 }
280 else
281 {
282 /* This is where the strings start. */
283 cache_data = (const char *) &cache->libs[cache->nlibs];
284
285 /* Now we can compute how large the string table is. */
286 cache_data_size = (const char *) cache + cachesize - cache_data;
287
288#undef HWCAP_CHECK
289#define HWCAP_CHECK do {} while (0)
290 SEARCH_CACHE (cache);
291 }
292
293 /* Print our result if wanted. */
294 if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
295 && best != NULL)
296 _dl_debug_printf (" trying file=%s\n", best);
297
298 if (best == NULL)
299 return NULL;
300
301 /* The double copy is *required* since malloc may be interposed
302 and call dlopen itself whose completion would unmap the data
303 we are accessing. Therefore we must make the copy of the
304 mapping data without using malloc. */
305 char *temp;
306 temp = alloca (strlen (best) + 1);
307 strcpy (temp, best);
308 return __strdup (temp);
309}
310
311#ifndef MAP_COPY
312/* If the system does not support MAP_COPY we cannot leave the file open
313 all the time since this would create problems when the file is replaced.
314 Therefore we provide this function to close the file and open it again
315 once needed. */
316void
317_dl_unload_cache (void)
318{
319 if (cache != NULL && cache != (struct cache_file *) -1)
320 {
321 __munmap (cache, cachesize);
322 cache = NULL;
323 }
324}
325#endif
326