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
24 #include <bionic/pthread_internal.h>
25 #include <private/bionic_tls.h>
26 #include <private/ScopedPthreadMutexLocker.h>
27 #include <private/ThreadLocalBuffer.h>
28
29 /* This file hijacks the symbols stubbed out in libdl.so. */
30
31 static pthread_mutex_t gDlMutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;
32
__bionic_set_dlerror(char * new_value)33 static const char* __bionic_set_dlerror(char* new_value) {
34 void* tls = const_cast<void*>(__get_tls());
35 char** dlerror_slot = &reinterpret_cast<char**>(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_update_LD_LIBRARY_PATH(const char * ld_library_path)58 void android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
59 ScopedPthreadMutexLocker locker(&gDlMutex);
60 do_android_update_LD_LIBRARY_PATH(ld_library_path);
61 }
62
dlopen(const char * filename,int flags)63 void* dlopen(const char* filename, int flags) {
64 ScopedPthreadMutexLocker locker(&gDlMutex);
65 soinfo* result = do_dlopen(filename, flags);
66 if (result == NULL) {
67 __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
68 return NULL;
69 }
70 return result;
71 }
72
dlsym(void * handle,const char * symbol)73 void* dlsym(void* handle, const char* symbol) {
74 ScopedPthreadMutexLocker locker(&gDlMutex);
75
76 if (handle == NULL) {
77 __bionic_format_dlerror("dlsym library handle is null", NULL);
78 return NULL;
79 }
80 if (symbol == NULL) {
81 __bionic_format_dlerror("dlsym symbol name is null", NULL);
82 return NULL;
83 }
84
85 soinfo* found = NULL;
86 Elf32_Sym* sym = NULL;
87 if (handle == RTLD_DEFAULT) {
88 sym = dlsym_linear_lookup(symbol, &found, NULL);
89 } else if (handle == RTLD_NEXT) {
90 void* ret_addr = __builtin_return_address(0);
91 soinfo* si = find_containing_library(ret_addr);
92
93 sym = NULL;
94 if (si && si->next) {
95 sym = dlsym_linear_lookup(symbol, &found, si->next);
96 }
97 } else {
98 found = reinterpret_cast<soinfo*>(handle);
99 sym = dlsym_handle_lookup(found, symbol);
100 }
101
102 if (sym != NULL) {
103 unsigned bind = ELF32_ST_BIND(sym->st_info);
104
105 if (bind == STB_GLOBAL && sym->st_shndx != 0) {
106 unsigned ret = sym->st_value + found->load_bias;
107 return (void*) ret;
108 }
109
110 __bionic_format_dlerror("symbol found but not global", symbol);
111 return NULL;
112 } else {
113 __bionic_format_dlerror("undefined symbol", symbol);
114 return NULL;
115 }
116 }
117
dladdr(const void * addr,Dl_info * info)118 int dladdr(const void* addr, Dl_info* info) {
119 ScopedPthreadMutexLocker locker(&gDlMutex);
120
121 // Determine if this address can be found in any library currently mapped.
122 soinfo* si = find_containing_library(addr);
123 if (si == NULL) {
124 return 0;
125 }
126
127 memset(info, 0, sizeof(Dl_info));
128
129 info->dli_fname = si->name;
130 // Address at which the shared object is loaded.
131 info->dli_fbase = (void*) si->base;
132
133 // Determine if any symbol in the library contains the specified address.
134 Elf32_Sym *sym = dladdr_find_symbol(si, addr);
135 if (sym != NULL) {
136 info->dli_sname = si->strtab + sym->st_name;
137 info->dli_saddr = (void*)(si->load_bias + sym->st_value);
138 }
139
140 return 1;
141 }
142
dlclose(void * handle)143 int dlclose(void* handle) {
144 ScopedPthreadMutexLocker locker(&gDlMutex);
145 return do_dlclose(reinterpret_cast<soinfo*>(handle));
146 }
147
148 #if defined(ANDROID_ARM_LINKER)
149 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667
150 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890
151 #define ANDROID_LIBDL_STRTAB \
152 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0dl_unwind_find_exidx\0"
153
154 #elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER)
155 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667
156 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890
157 #define ANDROID_LIBDL_STRTAB \
158 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0dl_iterate_phdr\0"
159 #else
160 #error Unsupported architecture. Only ARM, MIPS, and x86 are presently supported.
161 #endif
162
163 // name_offset: starting index of the name in libdl_info.strtab
164 #define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
165 { name_offset, \
166 reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
167 /* st_size */ 0, \
168 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
169 /* st_other */ 0, \
170 shndx }
171
172 static Elf32_Sym gLibDlSymtab[] = {
173 // Total length of libdl_info.strtab, including trailing 0.
174 // This is actually the STH_UNDEF entry. Technically, it's
175 // supposed to have st_name == 0, but instead, it points to an index
176 // in the strtab with a \0 to make iterating through the symtab easier.
177 ELF32_SYM_INITIALIZER(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
178 ELF32_SYM_INITIALIZER( 0, &dlopen, 1),
179 ELF32_SYM_INITIALIZER( 7, &dlclose, 1),
180 ELF32_SYM_INITIALIZER(15, &dlsym, 1),
181 ELF32_SYM_INITIALIZER(21, &dlerror, 1),
182 ELF32_SYM_INITIALIZER(29, &dladdr, 1),
183 ELF32_SYM_INITIALIZER(36, &android_update_LD_LIBRARY_PATH, 1),
184 #if defined(ANDROID_ARM_LINKER)
185 ELF32_SYM_INITIALIZER(67, &dl_unwind_find_exidx, 1),
186 #elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER)
187 ELF32_SYM_INITIALIZER(67, &dl_iterate_phdr, 1),
188 #endif
189 };
190
191 // Fake out a hash table with a single bucket.
192 // A search of the hash table will look through
193 // gLibDlSymtab starting with index [1], then
194 // use gLibDlChains to find the next index to
195 // look at. gLibDlChains should be set up to
196 // walk through every element in gLibDlSymtab,
197 // and then end with 0 (sentinel value).
198 //
199 // That is, gLibDlChains should look like
200 // { 0, 2, 3, ... N, 0 } where N is the number
201 // of actual symbols, or nelems(gLibDlSymtab)-1
202 // (since the first element of gLibDlSymtab is not
203 // a real symbol).
204 //
205 // (see soinfo_elf_lookup())
206 //
207 // Note that adding any new symbols here requires
208 // stubbing them out in libdl.
209 static unsigned gLibDlBuckets[1] = { 1 };
210 static unsigned gLibDlChains[8] = { 0, 2, 3, 4, 5, 6, 7, 0 };
211
212 // This is used by the dynamic linker. Every process gets these symbols for free.
213 soinfo libdl_info = {
214 "libdl.so",
215
216 phdr: 0, phnum: 0,
217 entry: 0, base: 0, size: 0,
218 unused1: 0, dynamic: 0, unused2: 0, unused3: 0,
219 next: 0,
220
221 flags: FLAG_LINKED,
222
223 strtab: ANDROID_LIBDL_STRTAB,
224 symtab: gLibDlSymtab,
225
226 nbucket: 1,
227 nchain: 8,
228 bucket: gLibDlBuckets,
229 chain: gLibDlChains,
230
231 plt_got: 0, plt_rel: 0, plt_rel_count: 0, rel: 0, rel_count: 0,
232 preinit_array: 0, preinit_array_count: 0, init_array: 0, init_array_count: 0,
233 fini_array: 0, fini_array_count: 0, init_func: 0, fini_func: 0,
234
235 #if defined(ANDROID_ARM_LINKER)
236 ARM_exidx: 0, ARM_exidx_count: 0,
237 #elif defined(ANDROID_MIPS_LINKER)
238 mips_symtabno: 0, mips_local_gotno: 0, mips_gotsym: 0,
239 #endif
240
241 ref_count: 0,
242 { l_addr: 0, l_name: 0, l_ld: 0, l_next: 0, l_prev: 0, },
243 constructors_called: false,
244 load_bias: 0,
245 has_text_relocations: false,
246 has_DT_SYMBOLIC: true,
247 };
248