1 /*
2 * Copyright (C) 2007 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
17 #include "linker.h"
19 #include <dlfcn.h>
20 #include <pthread.h>
21 #include <stdio.h>
22 #include <stdlib.h>
24 #include <bionic/pthread_internal.h>
25 #include "private/bionic_tls.h"
26 #include "private/ScopedPthreadMutexLocker.h"
27 #include "private/ThreadLocalBuffer.h"
29 /* This file hijacks the symbols stubbed out in libdl.so. */
31 static pthread_mutex_t gDlMutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;
33 static const char* __bionic_set_dlerror(char* new_value) {
34 char** dlerror_slot = &reinterpret_cast<char**>(__get_tls())[TLS_SLOT_DLERROR];
36 const char* old_value = *dlerror_slot;
37 *dlerror_slot = new_value;
38 return old_value;
39 }
41 static void __bionic_format_dlerror(const char* msg, const char* detail) {
42 char* buffer = __get_thread()->dlerror_buffer;
43 strlcpy(buffer, msg, __BIONIC_DLERROR_BUFFER_SIZE);
44 if (detail != NULL) {
45 strlcat(buffer, ": ", __BIONIC_DLERROR_BUFFER_SIZE);
46 strlcat(buffer, detail, __BIONIC_DLERROR_BUFFER_SIZE);
47 }
49 __bionic_set_dlerror(buffer);
50 }
52 const char* dlerror() {
53 const char* old_value = __bionic_set_dlerror(NULL);
54 return old_value;
55 }
57 void android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) {
58 ScopedPthreadMutexLocker locker(&gDlMutex);
59 do_android_get_LD_LIBRARY_PATH(buffer, buffer_size);
60 }
62 void android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
63 ScopedPthreadMutexLocker locker(&gDlMutex);
64 do_android_update_LD_LIBRARY_PATH(ld_library_path);
65 }
67 void* dlopen(const char* filename, int flags) {
68 ScopedPthreadMutexLocker locker(&gDlMutex);
69 soinfo* result = do_dlopen(filename, flags);
70 if (result == NULL) {
71 __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
72 return NULL;
73 }
74 return result;
75 }
77 void* dlsym(void* handle, const char* symbol) {
78 ScopedPthreadMutexLocker locker(&gDlMutex);
80 if (handle == NULL) {
81 __bionic_format_dlerror("dlsym library handle is null", NULL);
82 return NULL;
83 }
84 if (symbol == NULL) {
85 __bionic_format_dlerror("dlsym symbol name is null", NULL);
86 return NULL;
87 }
89 soinfo* found = NULL;
90 Elf_Sym* sym = NULL;
91 if (handle == RTLD_DEFAULT) {
92 sym = dlsym_linear_lookup(symbol, &found, NULL);
93 } else if (handle == RTLD_NEXT) {
94 void* ret_addr = __builtin_return_address(0);
95 soinfo* si = find_containing_library(ret_addr);
97 sym = NULL;
98 if (si && si->next) {
99 sym = dlsym_linear_lookup(symbol, &found, si->next);
100 }
101 } else {
102 found = reinterpret_cast<soinfo*>(handle);
103 sym = dlsym_handle_lookup(found, symbol);
104 }
106 if (sym != NULL) {
107 unsigned bind = ELF_ST_BIND(sym->st_info);
109 if (bind == STB_GLOBAL && sym->st_shndx != 0) {
110 return reinterpret_cast<void*>(sym->st_value + found->load_bias);
111 }
113 __bionic_format_dlerror("symbol found but not global", symbol);
114 return NULL;
115 } else {
116 __bionic_format_dlerror("undefined symbol", symbol);
117 return NULL;
118 }
119 }
121 int dladdr(const void* addr, Dl_info* info) {
122 ScopedPthreadMutexLocker locker(&gDlMutex);
124 // Determine if this address can be found in any library currently mapped.
125 soinfo* si = find_containing_library(addr);
126 if (si == NULL) {
127 return 0;
128 }
130 memset(info, 0, sizeof(Dl_info));
132 info->dli_fname = si->name;
133 // Address at which the shared object is loaded.
134 info->dli_fbase = (void*) si->base;
136 // Determine if any symbol in the library contains the specified address.
137 Elf_Sym *sym = dladdr_find_symbol(si, addr);
138 if (sym != NULL) {
139 info->dli_sname = si->strtab + sym->st_name;
140 info->dli_saddr = (void*)(si->load_bias + sym->st_value);
141 }
143 return 1;
144 }
146 int dlclose(void* handle) {
147 ScopedPthreadMutexLocker locker(&gDlMutex);
148 return do_dlclose(reinterpret_cast<soinfo*>(handle));
149 }
151 // name_offset: starting index of the name in libdl_info.strtab
152 #define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
153 { name_offset, \
154 reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
155 /* st_size */ 0, \
156 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
157 /* st_other */ 0, \
158 shndx, \
159 }
161 #define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
162 { name_offset, \
163 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
164 /* st_other */ 0, \
165 shndx, \
166 reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
167 /* st_size */ 0, \
168 }
170 #if defined(__LP64__)
171 # define ELF_SYM_INITIALIZER ELF64_SYM_INITIALIZER
172 #else
173 # define ELF_SYM_INITIALIZER ELF32_SYM_INITIALIZER
174 #endif
176 #if defined(__arm__)
177 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1
178 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1
179 # define ANDROID_LIBDL_STRTAB \
180 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0dl_unwind_find_exidx\0"
181 #elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
182 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1
183 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1
184 # define ANDROID_LIBDL_STRTAB \
185 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0"
186 #else
187 # error Unsupported architecture. Only arm, arm64, mips, x86, and x86_64 are presently supported.
188 #endif
190 static Elf_Sym gLibDlSymtab[] = {
191 // Total length of libdl_info.strtab, including trailing 0.
192 // This is actually the STH_UNDEF entry. Technically, it's
193 // supposed to have st_name == 0, but instead, it points to an index
194 // in the strtab with a \0 to make iterating through the symtab easier.
195 ELF_SYM_INITIALIZER(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
196 ELF_SYM_INITIALIZER( 0, &dlopen, 1),
197 ELF_SYM_INITIALIZER( 7, &dlclose, 1),
198 ELF_SYM_INITIALIZER( 15, &dlsym, 1),
199 ELF_SYM_INITIALIZER( 21, &dlerror, 1),
200 ELF_SYM_INITIALIZER( 29, &dladdr, 1),
201 ELF_SYM_INITIALIZER( 36, &android_update_LD_LIBRARY_PATH, 1),
202 ELF_SYM_INITIALIZER( 67, &android_get_LD_LIBRARY_PATH, 1),
203 ELF_SYM_INITIALIZER( 95, &dl_iterate_phdr, 1),
204 #if defined(__arm__)
205 ELF_SYM_INITIALIZER(111, &dl_unwind_find_exidx, 1),
206 #endif
207 };
209 // Fake out a hash table with a single bucket.
210 //
211 // A search of the hash table will look through gLibDlSymtab starting with index 1, then
212 // use gLibDlChains to find the next index to look at. gLibDlChains should be set up to
213 // walk through every element in gLibDlSymtab, and then end with 0 (sentinel value).
214 //
215 // That is, gLibDlChains should look like { 0, 2, 3, ... N, 0 } where N is the number
216 // of actual symbols, or nelems(gLibDlSymtab)-1 (since the first element of gLibDlSymtab is not
217 // a real symbol). (See soinfo_elf_lookup().)
218 //
219 // Note that adding any new symbols here requires stubbing them out in libdl.
220 static unsigned gLibDlBuckets[1] = { 1 };
221 #if defined(__arm__)
222 static unsigned gLibDlChains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
223 #else
224 static unsigned gLibDlChains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 0 };
225 #endif
227 // This is used by the dynamic linker. Every process gets these symbols for free.
228 soinfo libdl_info = {
229 "libdl.so",
231 .phdr = 0,
232 .phnum = 0,
233 .entry = 0,
234 .base = 0,
235 .size = 0,
237 #if !defined(__LP64__)
238 .unused1 = 0,
239 #endif
241 .dynamic = 0,
243 #if !defined(__LP64__)
244 .unused2 = 0, .unused3 = 0,
245 #endif
247 .next = 0,
249 .flags = FLAG_LINKED,
251 .strtab = ANDROID_LIBDL_STRTAB,
252 .symtab = gLibDlSymtab,
254 .nbucket = sizeof(gLibDlBuckets)/sizeof(unsigned),
255 .nchain = sizeof(gLibDlChains)/sizeof(unsigned),
256 .bucket = gLibDlBuckets,
257 .chain = gLibDlChains,
259 #if defined(USE_RELA)
260 .plt_rela = 0,
261 .plt_rela_count = 0,
262 .rela = 0,
263 .rela_count = 0,
264 #else
265 .plt_got = 0,
266 .plt_rel = 0,
267 .plt_rel_count = 0,
268 .rel = 0,
269 .rel_count = 0,
270 #endif
272 .preinit_array = 0,
273 .preinit_array_count = 0,
275 .init_array = 0,
276 .init_array_count = 0,
278 .fini_array = 0,
279 .fini_array_count = 0,
281 .init_func = 0,
282 .fini_func = 0,
284 #if defined(__arm__)
285 .ARM_exidx = 0,
286 .ARM_exidx_count = 0,
287 #elif defined(__mips__)
288 .mips_symtabno = 0,
289 .mips_local_gotno = 0,
290 .mips_gotsym = 0,
291 #endif
293 .ref_count = 0,
294 { .l_addr = 0, .l_name = 0, .l_ld = 0, .l_next = 0, .l_prev = 0, },
295 .constructors_called = false,
296 .load_bias = 0,
297 #if !defined(__LP64__)
298 .has_text_relocations = false,
299 #endif
300 .has_DT_SYMBOLIC = true,
301 };