dlfcn.cpp revision 04f7e3e955ba7de5f449c995e667659319dc1cce
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, const android_dlextinfo* extinfo) { 71 ScopedPthreadMutexLocker locker(&g_dl_mutex); 72 soinfo* result = do_dlopen(filename, flags, extinfo); 73 if (result == nullptr) { 74 __bionic_format_dlerror("dlopen failed", linker_get_error_buffer()); 75 return nullptr; 76 } 77 return result; 78} 79 80void* android_dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) { 81 return dlopen_ext(filename, flags, extinfo); 82} 83 84void* dlopen(const char* filename, int flags) { 85 return dlopen_ext(filename, flags, nullptr); 86} 87 88void* dlsym(void* handle, const char* symbol) { 89 ScopedPthreadMutexLocker locker(&g_dl_mutex); 90 91#if !defined(__LP64__) 92 if (handle == nullptr) { 93 __bionic_format_dlerror("dlsym library handle is null", nullptr); 94 return nullptr; 95 } 96#endif 97 98 if (symbol == nullptr) { 99 __bionic_format_dlerror("dlsym symbol name is null", nullptr); 100 return nullptr; 101 } 102 103 soinfo* found = nullptr; 104 const ElfW(Sym)* sym = nullptr; 105 void* caller_addr = __builtin_return_address(0); 106 soinfo* caller = find_containing_library(caller_addr); 107 108 if (handle == RTLD_DEFAULT || handle == RTLD_NEXT) { 109 sym = dlsym_linear_lookup(symbol, &found, caller, handle); 110 } else { 111 sym = dlsym_handle_lookup(reinterpret_cast<soinfo*>(handle), &found, symbol); 112 } 113 114 if (sym != nullptr) { 115 unsigned bind = ELF_ST_BIND(sym->st_info); 116 117 if ((bind == STB_GLOBAL || bind == STB_WEAK) && sym->st_shndx != 0) { 118 return reinterpret_cast<void*>(found->resolve_symbol_address(sym)); 119 } 120 121 __bionic_format_dlerror("symbol found but not global", symbol); 122 return nullptr; 123 } else { 124 __bionic_format_dlerror("undefined symbol", symbol); 125 return nullptr; 126 } 127} 128 129int dladdr(const void* addr, Dl_info* info) { 130 ScopedPthreadMutexLocker locker(&g_dl_mutex); 131 132 // Determine if this address can be found in any library currently mapped. 133 soinfo* si = find_containing_library(addr); 134 if (si == nullptr) { 135 return 0; 136 } 137 138 memset(info, 0, sizeof(Dl_info)); 139 140 info->dli_fname = si->get_realpath(); 141 // Address at which the shared object is loaded. 142 info->dli_fbase = reinterpret_cast<void*>(si->base); 143 144 // Determine if any symbol in the library contains the specified address. 145 ElfW(Sym)* sym = si->find_symbol_by_address(addr); 146 if (sym != nullptr) { 147 info->dli_sname = si->get_string(sym->st_name); 148 info->dli_saddr = reinterpret_cast<void*>(si->resolve_symbol_address(sym)); 149 } 150 151 return 1; 152} 153 154int dlclose(void* handle) { 155 ScopedPthreadMutexLocker locker(&g_dl_mutex); 156 do_dlclose(reinterpret_cast<soinfo*>(handle)); 157 // dlclose has no defined errors. 158 return 0; 159} 160 161void android_set_application_target_sdk_version(uint32_t target) { 162 // lock to avoid modification in the middle of dlopen. 163 ScopedPthreadMutexLocker locker(&g_dl_mutex); 164 set_application_target_sdk_version(target); 165} 166 167uint32_t android_get_application_target_sdk_version() { 168 return get_application_target_sdk_version(); 169} 170 171// name_offset: starting index of the name in libdl_info.strtab 172#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \ 173 { name_offset, \ 174 reinterpret_cast<Elf32_Addr>(value), \ 175 /* st_size */ 0, \ 176 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \ 177 /* st_other */ 0, \ 178 shndx, \ 179 } 180 181#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \ 182 { name_offset, \ 183 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \ 184 /* st_other */ 0, \ 185 shndx, \ 186 reinterpret_cast<Elf64_Addr>(value), \ 187 /* st_size */ 0, \ 188 } 189 190static const char ANDROID_LIBDL_STRTAB[] = 191 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 99999 192 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 56789 193 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_it" 194 // 00000000001 1111111112222222222 3333333333444444444455555555556666666666777 777777788888888889999999999 195 // 01234567890 1234567890123456789 0123456789012345678901234567890123456789012 345678901234567890123456789 196 "erate_phdr\0android_dlopen_ext\0android_set_application_target_sdk_version\0android_get_application_tar" 197 // 0000000000111111 198 // 0123456789012345 199 "get_sdk_version\0" 200#if defined(__arm__) 201 // 216 202 "dl_unwind_find_exidx\0" 203#endif 204 ; 205 206static ElfW(Sym) g_libdl_symtab[] = { 207 // Total length of libdl_info.strtab, including trailing 0. 208 // This is actually the STH_UNDEF entry. Technically, it's 209 // supposed to have st_name == 0, but instead, it points to an index 210 // in the strtab with a \0 to make iterating through the symtab easier. 211 ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, nullptr, 0), 212 ELFW(SYM_INITIALIZER)( 0, &dlopen, 1), 213 ELFW(SYM_INITIALIZER)( 7, &dlclose, 1), 214 ELFW(SYM_INITIALIZER)( 15, &dlsym, 1), 215 ELFW(SYM_INITIALIZER)( 21, &dlerror, 1), 216 ELFW(SYM_INITIALIZER)( 29, &dladdr, 1), 217 ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1), 218 ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1), 219 ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1), 220 ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1), 221 ELFW(SYM_INITIALIZER)(130, &android_set_application_target_sdk_version, 1), 222 ELFW(SYM_INITIALIZER)(173, &android_get_application_target_sdk_version, 1), 223#if defined(__arm__) 224 ELFW(SYM_INITIALIZER)(216, &dl_unwind_find_exidx, 1), 225#endif 226}; 227 228// Fake out a hash table with a single bucket. 229// 230// A search of the hash table will look through g_libdl_symtab starting with index 1, then 231// use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to 232// walk through every element in g_libdl_symtab, and then end with 0 (sentinel value). 233// 234// That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number 235// of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not 236// a real symbol). (See soinfo_elf_lookup().) 237// 238// Note that adding any new symbols here requires stubbing them out in libdl. 239static unsigned g_libdl_buckets[1] = { 1 }; 240#if defined(__arm__) 241static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0 }; 242#else 243static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 0 }; 244#endif 245 246static uint8_t __libdl_info_buf[sizeof(soinfo)] __attribute__((aligned(8))); 247static soinfo* __libdl_info = nullptr; 248 249// This is used by the dynamic linker. Every process gets these symbols for free. 250soinfo* get_libdl_info() { 251 if (__libdl_info == nullptr) { 252 __libdl_info = new (__libdl_info_buf) soinfo("libdl.so", nullptr, 0, RTLD_GLOBAL); 253 __libdl_info->flags_ |= FLAG_LINKED; 254 __libdl_info->strtab_ = ANDROID_LIBDL_STRTAB; 255 __libdl_info->symtab_ = g_libdl_symtab; 256 __libdl_info->nbucket_ = sizeof(g_libdl_buckets)/sizeof(unsigned); 257 __libdl_info->nchain_ = sizeof(g_libdl_chains)/sizeof(unsigned); 258 __libdl_info->bucket_ = g_libdl_buckets; 259 __libdl_info->chain_ = g_libdl_chains; 260 __libdl_info->ref_count_ = 1; 261 __libdl_info->strtab_size_ = sizeof(ANDROID_LIBDL_STRTAB); 262 __libdl_info->local_group_root_ = __libdl_info; 263 __libdl_info->soname_ = "libdl.so"; 264 __libdl_info->target_sdk_version_ = __ANDROID_API__; 265#if defined(__arm__) 266 strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_)); 267#endif 268 } 269 270 return __libdl_info; 271} 272