dlfcn.cpp revision e5cfafe3446a33b0c77416061d598bf76d580ee0
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 <string.h> 24#include <android/dlext.h> 25#include <android/api-level.h> 26 27#include <bionic/pthread_internal.h> 28#include "private/bionic_tls.h" 29#include "private/ScopedPthreadMutexLocker.h" 30#include "private/ThreadLocalBuffer.h" 31 32/* This file hijacks the symbols stubbed out in libdl.so. */ 33 34static pthread_mutex_t g_dl_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP; 35 36static const char* __bionic_set_dlerror(char* new_value) { 37 char** dlerror_slot = &reinterpret_cast<char**>(__get_tls())[TLS_SLOT_DLERROR]; 38 39 const char* old_value = *dlerror_slot; 40 *dlerror_slot = new_value; 41 return old_value; 42} 43 44static void __bionic_format_dlerror(const char* msg, const char* detail) { 45 char* buffer = __get_thread()->dlerror_buffer; 46 strlcpy(buffer, msg, __BIONIC_DLERROR_BUFFER_SIZE); 47 if (detail != nullptr) { 48 strlcat(buffer, ": ", __BIONIC_DLERROR_BUFFER_SIZE); 49 strlcat(buffer, detail, __BIONIC_DLERROR_BUFFER_SIZE); 50 } 51 52 __bionic_set_dlerror(buffer); 53} 54 55const char* dlerror() { 56 const char* old_value = __bionic_set_dlerror(nullptr); 57 return old_value; 58} 59 60void android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) { 61 ScopedPthreadMutexLocker locker(&g_dl_mutex); 62 do_android_get_LD_LIBRARY_PATH(buffer, buffer_size); 63} 64 65void android_update_LD_LIBRARY_PATH(const char* ld_library_path) { 66 ScopedPthreadMutexLocker locker(&g_dl_mutex); 67 do_android_update_LD_LIBRARY_PATH(ld_library_path); 68} 69 70static void* dlopen_ext(const char* filename, int flags, 71 const android_dlextinfo* extinfo, void* caller_addr) { 72 ScopedPthreadMutexLocker locker(&g_dl_mutex); 73 soinfo* caller = find_containing_library(caller_addr); 74 soinfo* result = do_dlopen(filename, flags, extinfo, caller); 75 if (result == nullptr) { 76 __bionic_format_dlerror("dlopen failed", linker_get_error_buffer()); 77 return nullptr; 78 } 79 return result; 80} 81 82void* android_dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) { 83 void* caller_addr = __builtin_return_address(0); 84 return dlopen_ext(filename, flags, extinfo, caller_addr); 85} 86 87void* dlopen(const char* filename, int flags) { 88 void* caller_addr = __builtin_return_address(0); 89 return dlopen_ext(filename, flags, nullptr, caller_addr); 90} 91 92void* dlsym(void* handle, const char* symbol) { 93 ScopedPthreadMutexLocker locker(&g_dl_mutex); 94 95#if !defined(__LP64__) 96 if (handle == nullptr) { 97 __bionic_format_dlerror("dlsym library handle is null", nullptr); 98 return nullptr; 99 } 100#endif 101 102 if (symbol == nullptr) { 103 __bionic_format_dlerror("dlsym symbol name is null", nullptr); 104 return nullptr; 105 } 106 107 soinfo* found = nullptr; 108 const ElfW(Sym)* sym = nullptr; 109 void* caller_addr = __builtin_return_address(0); 110 soinfo* caller = find_containing_library(caller_addr); 111 112 if (handle == RTLD_DEFAULT || handle == RTLD_NEXT) { 113 sym = dlsym_linear_lookup(symbol, &found, caller, handle); 114 } else { 115 sym = dlsym_handle_lookup(reinterpret_cast<soinfo*>(handle), &found, symbol); 116 } 117 118 if (sym != nullptr) { 119 unsigned bind = ELF_ST_BIND(sym->st_info); 120 121 if ((bind == STB_GLOBAL || bind == STB_WEAK) && sym->st_shndx != 0) { 122 return reinterpret_cast<void*>(found->resolve_symbol_address(sym)); 123 } 124 125 __bionic_format_dlerror("symbol found but not global", symbol); 126 return nullptr; 127 } else { 128 __bionic_format_dlerror("undefined symbol", symbol); 129 return nullptr; 130 } 131} 132 133int dladdr(const void* addr, Dl_info* info) { 134 ScopedPthreadMutexLocker locker(&g_dl_mutex); 135 136 // Determine if this address can be found in any library currently mapped. 137 soinfo* si = find_containing_library(addr); 138 if (si == nullptr) { 139 return 0; 140 } 141 142 memset(info, 0, sizeof(Dl_info)); 143 144 info->dli_fname = si->get_realpath(); 145 // Address at which the shared object is loaded. 146 info->dli_fbase = reinterpret_cast<void*>(si->base); 147 148 // Determine if any symbol in the library contains the specified address. 149 ElfW(Sym)* sym = si->find_symbol_by_address(addr); 150 if (sym != nullptr) { 151 info->dli_sname = si->get_string(sym->st_name); 152 info->dli_saddr = reinterpret_cast<void*>(si->resolve_symbol_address(sym)); 153 } 154 155 return 1; 156} 157 158int dlclose(void* handle) { 159 ScopedPthreadMutexLocker locker(&g_dl_mutex); 160 do_dlclose(reinterpret_cast<soinfo*>(handle)); 161 // dlclose has no defined errors. 162 return 0; 163} 164 165int dl_iterate_phdr(int (*cb)(dl_phdr_info* info, size_t size, void* data), void* data) { 166 ScopedPthreadMutexLocker locker(&g_dl_mutex); 167 return do_dl_iterate_phdr(cb, data); 168} 169 170void android_set_application_target_sdk_version(uint32_t target) { 171 // lock to avoid modification in the middle of dlopen. 172 ScopedPthreadMutexLocker locker(&g_dl_mutex); 173 set_application_target_sdk_version(target); 174} 175 176uint32_t android_get_application_target_sdk_version() { 177 return get_application_target_sdk_version(); 178} 179 180// name_offset: starting index of the name in libdl_info.strtab 181#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \ 182 { name_offset, \ 183 reinterpret_cast<Elf32_Addr>(value), \ 184 /* st_size */ 0, \ 185 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \ 186 /* st_other */ 0, \ 187 shndx, \ 188 } 189 190#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \ 191 { name_offset, \ 192 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \ 193 /* st_other */ 0, \ 194 shndx, \ 195 reinterpret_cast<Elf64_Addr>(value), \ 196 /* st_size */ 0, \ 197 } 198 199static const char ANDROID_LIBDL_STRTAB[] = 200 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 99999 201 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 56789 202 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_it" 203 // 00000000001 1111111112222222222 3333333333444444444455555555556666666666777 777777788888888889999999999 204 // 01234567890 1234567890123456789 0123456789012345678901234567890123456789012 345678901234567890123456789 205 "erate_phdr\0android_dlopen_ext\0android_set_application_target_sdk_version\0android_get_application_tar" 206 // 0000000000111111 207 // 0123456789012345 208 "get_sdk_version\0" 209#if defined(__arm__) 210 // 216 211 "dl_unwind_find_exidx\0" 212#endif 213 ; 214 215static ElfW(Sym) g_libdl_symtab[] = { 216 // Total length of libdl_info.strtab, including trailing 0. 217 // This is actually the STH_UNDEF entry. Technically, it's 218 // supposed to have st_name == 0, but instead, it points to an index 219 // in the strtab with a \0 to make iterating through the symtab easier. 220 ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, nullptr, 0), 221 ELFW(SYM_INITIALIZER)( 0, &dlopen, 1), 222 ELFW(SYM_INITIALIZER)( 7, &dlclose, 1), 223 ELFW(SYM_INITIALIZER)( 15, &dlsym, 1), 224 ELFW(SYM_INITIALIZER)( 21, &dlerror, 1), 225 ELFW(SYM_INITIALIZER)( 29, &dladdr, 1), 226 ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1), 227 ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1), 228 ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1), 229 ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1), 230 ELFW(SYM_INITIALIZER)(130, &android_set_application_target_sdk_version, 1), 231 ELFW(SYM_INITIALIZER)(173, &android_get_application_target_sdk_version, 1), 232#if defined(__arm__) 233 ELFW(SYM_INITIALIZER)(216, &dl_unwind_find_exidx, 1), 234#endif 235}; 236 237// Fake out a hash table with a single bucket. 238// 239// A search of the hash table will look through g_libdl_symtab starting with index 1, then 240// use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to 241// walk through every element in g_libdl_symtab, and then end with 0 (sentinel value). 242// 243// That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number 244// of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not 245// a real symbol). (See soinfo_elf_lookup().) 246// 247// Note that adding any new symbols here requires stubbing them out in libdl. 248static unsigned g_libdl_buckets[1] = { 1 }; 249#if defined(__arm__) 250static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0 }; 251#else 252static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 0 }; 253#endif 254 255static uint8_t __libdl_info_buf[sizeof(soinfo)] __attribute__((aligned(8))); 256static soinfo* __libdl_info = nullptr; 257 258// This is used by the dynamic linker. Every process gets these symbols for free. 259soinfo* get_libdl_info() { 260 if (__libdl_info == nullptr) { 261 __libdl_info = new (__libdl_info_buf) soinfo("libdl.so", nullptr, 0, RTLD_GLOBAL); 262 __libdl_info->flags_ |= FLAG_LINKED; 263 __libdl_info->strtab_ = ANDROID_LIBDL_STRTAB; 264 __libdl_info->symtab_ = g_libdl_symtab; 265 __libdl_info->nbucket_ = sizeof(g_libdl_buckets)/sizeof(unsigned); 266 __libdl_info->nchain_ = sizeof(g_libdl_chains)/sizeof(unsigned); 267 __libdl_info->bucket_ = g_libdl_buckets; 268 __libdl_info->chain_ = g_libdl_chains; 269 __libdl_info->ref_count_ = 1; 270 __libdl_info->strtab_size_ = sizeof(ANDROID_LIBDL_STRTAB); 271 __libdl_info->local_group_root_ = __libdl_info; 272 __libdl_info->soname_ = "libdl.so"; 273 __libdl_info->target_sdk_version_ = __ANDROID_API__; 274#if defined(__arm__) 275 strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_)); 276#endif 277 } 278 279 return __libdl_info; 280} 281