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 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 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 53 const char* dlerror() { 54 const char* old_value = __bionic_set_dlerror(NULL); 55 return old_value; 56 } 57 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 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 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 } 117 118 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 } 142 143 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
