1/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
2 Copyright (C) 1996-2016 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
28#ifndef _DL_PLATFORMS_COUNT
29# define _DL_PLATFORMS_COUNT 0
30#endif
31
32/* This is the starting address and the size of the mmap()ed file. */
33static struct cache_file *cache;
34static struct cache_file_new *cache_new;
35static size_t cachesize;
36
37/* 1 if cache_data + PTR points into the cache. */
38#define _dl_cache_verify_ptr(ptr) (ptr < cache_data_size)
39
40#define SEARCH_CACHE(cache) \
41/* We use binary search since the table is sorted in the cache file. \
42 The first matching entry in the table is returned. \
43 It is important to use the same algorithm as used while generating \
44 the cache file. */ \
45do \
46 { \
47 left = 0; \
48 right = cache->nlibs - 1; \
49 \
50 while (left <= right) \
51 { \
52 __typeof__ (cache->libs[0].key) key; \
53 \
54 middle = (left + right) / 2; \
55 \
56 key = cache->libs[middle].key; \
57 \
58 /* Make sure string table indices are not bogus before using \
59 them. */ \
60 if (! _dl_cache_verify_ptr (key)) \
61 { \
62 cmpres = 1; \
63 break; \
64 } \
65 \
66 /* Actually compare the entry with the key. */ \
67 cmpres = _dl_cache_libcmp (name, cache_data + key); \
68 if (__glibc_unlikely (cmpres == 0)) \
69 { \
70 /* Found it. LEFT now marks the last entry for which we \
71 know the name is correct. */ \
72 left = middle; \
73 \
74 /* There might be entries with this name before the one we \
75 found. So we have to find the beginning. */ \
76 while (middle > 0) \
77 { \
78 __typeof__ (cache->libs[0].key) key; \
79 \
80 key = cache->libs[middle - 1].key; \
81 /* Make sure string table indices are not bogus before \
82 using them. */ \
83 if (! _dl_cache_verify_ptr (key) \
84 /* Actually compare the entry. */ \
85 || _dl_cache_libcmp (name, cache_data + key) != 0) \
86 break; \
87 --middle; \
88 } \
89 \
90 do \
91 { \
92 int flags; \
93 __typeof__ (cache->libs[0]) *lib = &cache->libs[middle]; \
94 \
95 /* Only perform the name test if necessary. */ \
96 if (middle > left \
97 /* We haven't seen this string so far. Test whether the \
98 index is ok and whether the name matches. Otherwise \
99 we are done. */ \
100 && (! _dl_cache_verify_ptr (lib->key) \
101 || (_dl_cache_libcmp (name, cache_data + lib->key) \
102 != 0))) \
103 break; \
104 \
105 flags = lib->flags; \
106 if (_dl_cache_check_flags (flags) \
107 && _dl_cache_verify_ptr (lib->value)) \
108 { \
109 if (best == NULL || flags == GLRO(dl_correct_cache_id)) \
110 { \
111 HWCAP_CHECK; \
112 best = cache_data + lib->value; \
113 \
114 if (flags == GLRO(dl_correct_cache_id)) \
115 /* We've found an exact match for the shared \
116 object and no general `ELF' release. Stop \
117 searching. */ \
118 break; \
119 } \
120 } \
121 } \
122 while (++middle <= right); \
123 break; \
124 } \
125 \
126 if (cmpres < 0) \
127 left = middle + 1; \
128 else \
129 right = middle - 1; \
130 } \
131 } \
132while (0)
133
134
135int
136internal_function
137_dl_cache_libcmp (const char *p1, const char *p2)
138{
139 while (*p1 != '\0')
140 {
141 if (*p1 >= '0' && *p1 <= '9')
142 {
143 if (*p2 >= '0' && *p2 <= '9')
144 {
145 /* Must compare this numerically. */
146 int val1;
147 int val2;
148
149 val1 = *p1++ - '0';
150 val2 = *p2++ - '0';
151 while (*p1 >= '0' && *p1 <= '9')
152 val1 = val1 * 10 + *p1++ - '0';
153 while (*p2 >= '0' && *p2 <= '9')
154 val2 = val2 * 10 + *p2++ - '0';
155 if (val1 != val2)
156 return val1 - val2;
157 }
158 else
159 return 1;
160 }
161 else if (*p2 >= '0' && *p2 <= '9')
162 return -1;
163 else if (*p1 != *p2)
164 return *p1 - *p2;
165 else
166 {
167 ++p1;
168 ++p2;
169 }
170 }
171 return *p1 - *p2;
172}
173
174
175/* Look up NAME in ld.so.cache and return the file name stored there, or null
176 if none is found. The cache is loaded if it was not already. If loading
177 the cache previously failed there will be no more attempts to load it.
178 The caller is responsible for freeing the returned string. The ld.so.cache
179 may be unmapped at any time by a completing recursive dlopen and
180 this function must take care that it does not return references to
181 any data in the mapping. */
182char *
183internal_function
184_dl_load_cache_lookup (const char *name)
185{
186 int left, right, middle;
187 int cmpres;
188 const char *cache_data;
189 uint32_t cache_data_size;
190 const char *best;
191
192 /* Print a message if the loading of libs is traced. */
193 if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
194 _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
195
196 if (cache == NULL)
197 {
198 /* Read the contents of the file. */
199 void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
200 PROT_READ);
201
202 /* We can handle three different cache file formats here:
203 - the old libc5/glibc2.0/2.1 format
204 - the old format with the new format in it
205 - only the new format
206 The following checks if the cache contains any of these formats. */
207 if (file != MAP_FAILED && cachesize > sizeof *cache
208 && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0)
209 {
210 size_t offset;
211 /* Looks ok. */
212 cache = file;
213
214 /* Check for new version. */
215 offset = ALIGN_CACHE (sizeof (struct cache_file)
216 + cache->nlibs * sizeof (struct file_entry));
217
218 cache_new = (struct cache_file_new *) ((void *) cache + offset);
219 if (cachesize < (offset + sizeof (struct cache_file_new))
220 || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
221 sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
222 cache_new = (void *) -1;
223 }
224 else if (file != MAP_FAILED && cachesize > sizeof *cache_new
225 && memcmp (file, CACHEMAGIC_VERSION_NEW,
226 sizeof CACHEMAGIC_VERSION_NEW - 1) == 0)
227 {
228 cache_new = file;
229 cache = file;
230 }
231 else
232 {
233 if (file != MAP_FAILED)
234 __munmap (file, cachesize);
235 cache = (void *) -1;
236 }
237
238 assert (cache != NULL);
239 }
240
241 if (cache == (void *) -1)
242 /* Previously looked for the cache file and didn't find it. */
243 return NULL;
244
245 best = NULL;
246
247 if (cache_new != (void *) -1)
248 {
249 uint64_t platform;
250
251 /* This is where the strings start. */
252 cache_data = (const char *) cache_new;
253
254 /* Now we can compute how large the string table is. */
255 cache_data_size = (const char *) cache + cachesize - cache_data;
256
257 platform = _dl_string_platform (GLRO(dl_platform));
258 if (platform != (uint64_t) -1)
259 platform = 1ULL << platform;
260
261#define _DL_HWCAP_TLS_MASK (1LL << 63)
262 uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & GLRO(dl_hwcap_mask))
263 | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
264
265 /* Only accept hwcap if it's for the right platform. */
266#define HWCAP_CHECK \
267 if (lib->hwcap & hwcap_exclude) \
268 continue; \
269 if (GLRO(dl_osversion) && lib->osversion > GLRO(dl_osversion)) \
270 continue; \
271 if (_DL_PLATFORMS_COUNT \
272 && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0 \
273 && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform) \
274 continue
275 SEARCH_CACHE (cache_new);
276 }
277 else
278 {
279 /* This is where the strings start. */
280 cache_data = (const char *) &cache->libs[cache->nlibs];
281
282 /* Now we can compute how large the string table is. */
283 cache_data_size = (const char *) cache + cachesize - cache_data;
284
285#undef HWCAP_CHECK
286#define HWCAP_CHECK do {} while (0)
287 SEARCH_CACHE (cache);
288 }
289
290 /* Print our result if wanted. */
291 if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
292 && best != NULL)
293 _dl_debug_printf (" trying file=%s\n", best);
294
295 if (best == NULL)
296 return NULL;
297
298 /* The double copy is *required* since malloc may be interposed
299 and call dlopen itself whose completion would unmap the data
300 we are accessing. Therefore we must make the copy of the
301 mapping data without using malloc. */
302 char *temp;
303 temp = alloca (strlen (best) + 1);
304 strcpy (temp, best);
305 return strdup (temp);
306}
307
308#ifndef MAP_COPY
309/* If the system does not support MAP_COPY we cannot leave the file open
310 all the time since this would create problems when the file is replaced.
311 Therefore we provide this function to close the file and open it again
312 once needed. */
313void
314_dl_unload_cache (void)
315{
316 if (cache != NULL && cache != (struct cache_file *) -1)
317 {
318 __munmap (cache, cachesize);
319 cache = NULL;
320 }
321}
322#endif
323