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 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 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 != nullptr) { 46 strlcat(buffer, ": ", __BIONIC_DLERROR_BUFFER_SIZE); 47 strlcat(buffer, detail, __BIONIC_DLERROR_BUFFER_SIZE); 48 } 49 50 __bionic_set_dlerror(buffer); 51 } 52 53 const char* dlerror() { 54 const char* old_value = __bionic_set_dlerror(nullptr); 55 return old_value; 56 } 57 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 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 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 == nullptr) { 72 __bionic_format_dlerror("dlopen failed", linker_get_error_buffer()); 73 return nullptr; 74 } 75 return result; 76 } 77 78 void* android_dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) { 79 return dlopen_ext(filename, flags, extinfo); 80 } 81 82 void* dlopen(const char* filename, int flags) { 83 return dlopen_ext(filename, flags, nullptr); 84 } 85 86 void* dlsym(void* handle, const char* symbol) { 87 ScopedPthreadMutexLocker locker(&g_dl_mutex); 88 89 #if !defined(__LP64__) 90 if (handle == nullptr) { 91 __bionic_format_dlerror("dlsym library handle is null", nullptr); 92 return nullptr; 93 } 94 #endif 95 96 if (symbol == nullptr) { 97 __bionic_format_dlerror("dlsym symbol name is null", nullptr); 98 return nullptr; 99 } 100 101 soinfo* found = nullptr; 102 ElfW(Sym)* sym = nullptr; 103 if (handle == RTLD_DEFAULT) { 104 sym = dlsym_linear_lookup(symbol, &found, nullptr); 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 = nullptr; 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 != nullptr) { 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*>(found->resolve_symbol_address(sym)); 122 } 123 124 __bionic_format_dlerror("symbol found but not global", symbol); 125 return nullptr; 126 } else { 127 __bionic_format_dlerror("undefined symbol", symbol); 128 return nullptr; 129 } 130 } 131 132 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 == nullptr) { 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 != nullptr) { 150 info->dli_sname = si->get_string(sym->st_name); 151 info->dli_saddr = reinterpret_cast<void*>(si->resolve_symbol_address(sym)); 152 } 153 154 return 1; 155 } 156 157 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>(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>(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, nullptr, 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 static soinfo __libdl_info("libdl.so", nullptr, 0); 236 237 // This is used by the dynamic linker. Every process gets these symbols for free. 238 soinfo* get_libdl_info() { 239 if ((__libdl_info.flags & FLAG_LINKED) == 0) { 240 __libdl_info.flags |= FLAG_LINKED; 241 __libdl_info.strtab = ANDROID_LIBDL_STRTAB; 242 __libdl_info.symtab = g_libdl_symtab; 243 __libdl_info.nbucket = sizeof(g_libdl_buckets)/sizeof(unsigned); 244 __libdl_info.nchain = sizeof(g_libdl_chains)/sizeof(unsigned); 245 __libdl_info.bucket = g_libdl_buckets; 246 __libdl_info.chain = g_libdl_chains; 247 __libdl_info.ref_count = 1; 248 __libdl_info.strtab_size = sizeof(ANDROID_LIBDL_STRTAB); 249 } 250 251 return &__libdl_info; 252 } 253
