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 */
16
17 #include "linker.h"
18
19 #include <dlfcn.h>
20 #include <pthread.h>
21 #include <stdio.h>
22 #include <stdlib.h>
23 #include <android/dlext.h>
24
25 #include <bionic/pthread_internal.h>
26 #include "private/bionic_tls.h"
27 #include "private/ScopedPthreadMutexLocker.h"
28 #include "private/ThreadLocalBuffer.h"
29
30 /* This file hijacks the symbols stubbed out in libdl.so. */
31
32 static pthread_mutex_t g_dl_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;
33
__bionic_set_dlerror(char * new_value)34 static const char* __bionic_set_dlerror(char* new_value) {
35 char** dlerror_slot = &reinterpret_cast<char**>(__get_tls())[TLS_SLOT_DLERROR];
36
37 const char* old_value = *dlerror_slot;
38 *dlerror_slot = new_value;
39 return old_value;
40 }
41
__bionic_format_dlerror(const char * msg,const char * detail)42 static void __bionic_format_dlerror(const char* msg, const char* detail) {
43 char* buffer = __get_thread()->dlerror_buffer;
44 strlcpy(buffer, msg, __BIONIC_DLERROR_BUFFER_SIZE);
45 if (detail != NULL) {
46 strlcat(buffer, ": ", __BIONIC_DLERROR_BUFFER_SIZE);
47 strlcat(buffer, detail, __BIONIC_DLERROR_BUFFER_SIZE);
48 }
49
50 __bionic_set_dlerror(buffer);
51 }
52
dlerror()53 const char* dlerror() {
54 const char* old_value = __bionic_set_dlerror(NULL);
55 return old_value;
56 }
57
android_get_LD_LIBRARY_PATH(char * buffer,size_t buffer_size)58 void android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) {
59 ScopedPthreadMutexLocker locker(&g_dl_mutex);
60 do_android_get_LD_LIBRARY_PATH(buffer, buffer_size);
61 }
62
android_update_LD_LIBRARY_PATH(const char * ld_library_path)63 void android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
64 ScopedPthreadMutexLocker locker(&g_dl_mutex);
65 do_android_update_LD_LIBRARY_PATH(ld_library_path);
66 }
67
dlopen_ext(const char * filename,int flags,const android_dlextinfo * extinfo)68 static void* dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) {
69 ScopedPthreadMutexLocker locker(&g_dl_mutex);
70 soinfo* result = do_dlopen(filename, flags, extinfo);
71 if (result == NULL) {
72 __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
73 return NULL;
74 }
75 return result;
76 }
77
android_dlopen_ext(const char * filename,int flags,const android_dlextinfo * extinfo)78 void* android_dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) {
79 return dlopen_ext(filename, flags, extinfo);
80 }
81
dlopen(const char * filename,int flags)82 void* dlopen(const char* filename, int flags) {
83 return dlopen_ext(filename, flags, NULL);
84 }
85
dlsym(void * handle,const char * symbol)86 void* dlsym(void* handle, const char* symbol) {
87 ScopedPthreadMutexLocker locker(&g_dl_mutex);
88
89 #if !defined(__LP64__)
90 if (handle == NULL) {
91 __bionic_format_dlerror("dlsym library handle is null", NULL);
92 return NULL;
93 }
94 #endif
95
96 if (symbol == NULL) {
97 __bionic_format_dlerror("dlsym symbol name is null", NULL);
98 return NULL;
99 }
100
101 soinfo* found = NULL;
102 ElfW(Sym)* sym = NULL;
103 if (handle == RTLD_DEFAULT) {
104 sym = dlsym_linear_lookup(symbol, &found, NULL);
105 } else if (handle == RTLD_NEXT) {
106 void* caller_addr = __builtin_return_address(0);
107 soinfo* si = find_containing_library(caller_addr);
108
109 sym = NULL;
110 if (si && si->next) {
111 sym = dlsym_linear_lookup(symbol, &found, si->next);
112 }
113 } else {
114 sym = dlsym_handle_lookup(reinterpret_cast<soinfo*>(handle), &found, symbol);
115 }
116
117 if (sym != NULL) {
118 unsigned bind = ELF_ST_BIND(sym->st_info);
119
120 if ((bind == STB_GLOBAL || bind == STB_WEAK) && sym->st_shndx != 0) {
121 return reinterpret_cast<void*>(sym->st_value + found->load_bias);
122 }
123
124 __bionic_format_dlerror("symbol found but not global", symbol);
125 return NULL;
126 } else {
127 __bionic_format_dlerror("undefined symbol", symbol);
128 return NULL;
129 }
130 }
131
dladdr(const void * addr,Dl_info * info)132 int dladdr(const void* addr, Dl_info* info) {
133 ScopedPthreadMutexLocker locker(&g_dl_mutex);
134
135 // Determine if this address can be found in any library currently mapped.
136 soinfo* si = find_containing_library(addr);
137 if (si == NULL) {
138 return 0;
139 }
140
141 memset(info, 0, sizeof(Dl_info));
142
143 info->dli_fname = si->name;
144 // Address at which the shared object is loaded.
145 info->dli_fbase = reinterpret_cast<void*>(si->base);
146
147 // Determine if any symbol in the library contains the specified address.
148 ElfW(Sym)* sym = dladdr_find_symbol(si, addr);
149 if (sym != NULL) {
150 info->dli_sname = si->strtab + sym->st_name;
151 info->dli_saddr = reinterpret_cast<void*>(si->load_bias + sym->st_value);
152 }
153
154 return 1;
155 }
156
dlclose(void * handle)157 int dlclose(void* handle) {
158 ScopedPthreadMutexLocker locker(&g_dl_mutex);
159 do_dlclose(reinterpret_cast<soinfo*>(handle));
160 // dlclose has no defined errors.
161 return 0;
162 }
163
164 // name_offset: starting index of the name in libdl_info.strtab
165 #define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
166 { name_offset, \
167 reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
168 /* st_size */ 0, \
169 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
170 /* st_other */ 0, \
171 shndx, \
172 }
173
174 #define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
175 { name_offset, \
176 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
177 /* st_other */ 0, \
178 shndx, \
179 reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
180 /* st_size */ 0, \
181 }
182
183 #if defined(__arm__)
184 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222 333333333344444444445
185 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789 012345678901234567890
186 # define ANDROID_LIBDL_STRTAB \
187 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0android_dlopen_ext\0dl_unwind_find_exidx\0"
188 #elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
189 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222
190 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789
191 # define ANDROID_LIBDL_STRTAB \
192 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0android_dlopen_ext\0"
193 #else
194 # error Unsupported architecture. Only arm, arm64, mips, mips64, x86 and x86_64 are presently supported.
195 #endif
196
197 static ElfW(Sym) g_libdl_symtab[] = {
198 // Total length of libdl_info.strtab, including trailing 0.
199 // This is actually the STH_UNDEF entry. Technically, it's
200 // supposed to have st_name == 0, but instead, it points to an index
201 // in the strtab with a \0 to make iterating through the symtab easier.
202 ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
203 ELFW(SYM_INITIALIZER)( 0, &dlopen, 1),
204 ELFW(SYM_INITIALIZER)( 7, &dlclose, 1),
205 ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
206 ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
207 ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
208 ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
209 ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
210 ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
211 ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1),
212 #if defined(__arm__)
213 ELFW(SYM_INITIALIZER)(130, &dl_unwind_find_exidx, 1),
214 #endif
215 };
216
217 // Fake out a hash table with a single bucket.
218 //
219 // A search of the hash table will look through g_libdl_symtab starting with index 1, then
220 // use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to
221 // walk through every element in g_libdl_symtab, and then end with 0 (sentinel value).
222 //
223 // That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number
224 // of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not
225 // a real symbol). (See soinfo_elf_lookup().)
226 //
227 // Note that adding any new symbols here requires stubbing them out in libdl.
228 static unsigned g_libdl_buckets[1] = { 1 };
229 #if defined(__arm__)
230 static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0 };
231 #else
232 static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
233 #endif
234
235 // Defined as global because we do not yet have access
236 // to synchronization functions __cxa_guard_* needed
237 // to define statics inside functions.
238 static soinfo __libdl_info;
239
240 // This is used by the dynamic linker. Every process gets these symbols for free.
get_libdl_info()241 soinfo* get_libdl_info() {
242 if (__libdl_info.name[0] == '\0') {
243 // initialize
244 strncpy(__libdl_info.name, "libdl.so", sizeof(__libdl_info.name));
245 __libdl_info.flags = FLAG_LINKED | FLAG_NEW_SOINFO;
246 __libdl_info.strtab = ANDROID_LIBDL_STRTAB;
247 __libdl_info.symtab = g_libdl_symtab;
248 __libdl_info.nbucket = sizeof(g_libdl_buckets)/sizeof(unsigned);
249 __libdl_info.nchain = sizeof(g_libdl_chains)/sizeof(unsigned);
250 __libdl_info.bucket = g_libdl_buckets;
251 __libdl_info.chain = g_libdl_chains;
252 __libdl_info.has_DT_SYMBOLIC = true;
253 }
254
255 return &__libdl_info;
256 }
257