dlfcn.cpp revision d97e9f546ea195686a78e539315b273393609b9e
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 32static pthread_mutex_t g_dl_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER; 33 34static 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 42static 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 53const char* dlerror() { 54 const char* old_value = __bionic_set_dlerror(NULL); 55 return old_value; 56} 57 58void 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 63void 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 68static 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 == NULL) { 72 __bionic_format_dlerror("dlopen failed", linker_get_error_buffer()); 73 return NULL; 74 } 75 return result; 76} 77 78void* android_dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) { 79 return dlopen_ext(filename, flags, extinfo); 80} 81 82void* dlopen(const char* filename, int flags) { 83 return dlopen_ext(filename, flags, NULL); 84} 85 86void* dlsym(void* handle, const char* symbol) { 87 ScopedPthreadMutexLocker locker(&g_dl_mutex); 88 89#if !defined(__LP64__) 90 if (handle == NULL) { 91 __bionic_format_dlerror("dlsym library handle is null", NULL); 92 return NULL; 93 } 94#endif 95 96 if (symbol == NULL) { 97 __bionic_format_dlerror("dlsym symbol name is null", NULL); 98 return NULL; 99 } 100 101 soinfo* found = NULL; 102 ElfW(Sym)* sym = NULL; 103 void* caller_addr = __builtin_return_address(0); 104 soinfo* caller_si = find_containing_library(caller_addr); 105 106 if (handle == RTLD_DEFAULT) { 107 sym = dlsym_linear_lookup(symbol, &found, NULL, caller_si); 108 } else if (handle == RTLD_NEXT) { 109 sym = NULL; 110 if (caller_si && caller_si->next) { 111 sym = dlsym_linear_lookup(symbol, &found, caller_si->next, caller_si); 112 } 113 } else { 114 found = reinterpret_cast<soinfo*>(handle); 115 sym = dlsym_handle_lookup(found, symbol, caller_si); 116 } 117 118 if (sym != NULL && sym->st_shndx != 0) { 119 return reinterpret_cast<void*>(sym->st_value + found->load_bias); 120 } else { 121 __bionic_format_dlerror("undefined symbol", symbol); 122 return NULL; 123 } 124} 125 126int dladdr(const void* addr, Dl_info* info) { 127 ScopedPthreadMutexLocker locker(&g_dl_mutex); 128 129 // Determine if this address can be found in any library currently mapped. 130 soinfo* si = find_containing_library(addr); 131 if (si == NULL) { 132 return 0; 133 } 134 135 memset(info, 0, sizeof(Dl_info)); 136 137 info->dli_fname = si->name; 138 // Address at which the shared object is loaded. 139 info->dli_fbase = reinterpret_cast<void*>(si->base); 140 141 // Determine if any symbol in the library contains the specified address. 142 ElfW(Sym)* sym = dladdr_find_symbol(si, addr); 143 if (sym != NULL) { 144 info->dli_sname = si->strtab + sym->st_name; 145 info->dli_saddr = reinterpret_cast<void*>(si->load_bias + sym->st_value); 146 } 147 148 return 1; 149} 150 151int dlclose(void* handle) { 152 ScopedPthreadMutexLocker locker(&g_dl_mutex); 153 do_dlclose(reinterpret_cast<soinfo*>(handle)); 154 // dlclose has no defined errors. 155 return 0; 156} 157 158// name_offset: starting index of the name in libdl_info.strtab 159#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \ 160 { name_offset, \ 161 reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \ 162 /* st_size */ 0, \ 163 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \ 164 /* st_other */ 0, \ 165 shndx, \ 166 } 167 168#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \ 169 { name_offset, \ 170 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \ 171 /* st_other */ 0, \ 172 shndx, \ 173 reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \ 174 /* st_size */ 0, \ 175 } 176 177#if defined(__arm__) 178 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222 333333333344444444445 179 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789 012345678901234567890 180# define ANDROID_LIBDL_STRTAB \ 181 "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" 182#elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__) 183 // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222 184 // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789 185# define ANDROID_LIBDL_STRTAB \ 186 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0android_dlopen_ext\0" 187#else 188# error Unsupported architecture. Only arm, arm64, mips, mips64, x86 and x86_64 are presently supported. 189#endif 190 191static ElfW(Sym) g_libdl_symtab[] = { 192 // Total length of libdl_info.strtab, including trailing 0. 193 // This is actually the STH_UNDEF entry. Technically, it's 194 // supposed to have st_name == 0, but instead, it points to an index 195 // in the strtab with a \0 to make iterating through the symtab easier. 196 ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0), 197 ELFW(SYM_INITIALIZER)( 0, &dlopen, 1), 198 ELFW(SYM_INITIALIZER)( 7, &dlclose, 1), 199 ELFW(SYM_INITIALIZER)( 15, &dlsym, 1), 200 ELFW(SYM_INITIALIZER)( 21, &dlerror, 1), 201 ELFW(SYM_INITIALIZER)( 29, &dladdr, 1), 202 ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1), 203 ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1), 204 ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1), 205 ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1), 206#if defined(__arm__) 207 ELFW(SYM_INITIALIZER)(130, &dl_unwind_find_exidx, 1), 208#endif 209}; 210 211// Fake out a hash table with a single bucket. 212// 213// A search of the hash table will look through g_libdl_symtab starting with index 1, then 214// use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to 215// walk through every element in g_libdl_symtab, and then end with 0 (sentinel value). 216// 217// That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number 218// of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not 219// a real symbol). (See soinfo_elf_lookup().) 220// 221// Note that adding any new symbols here requires stubbing them out in libdl. 222static unsigned g_libdl_buckets[1] = { 1 }; 223#if defined(__arm__) 224static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0 }; 225#else 226static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 }; 227#endif 228 229// Defined as global because we do not yet have access 230// to synchronization functions __cxa_guard_* needed 231// to define statics inside functions. 232static soinfo __libdl_info; 233 234// This is used by the dynamic linker. Every process gets these symbols for free. 235soinfo* get_libdl_info() { 236 if (__libdl_info.name[0] == '\0') { 237 // initialize 238 strncpy(__libdl_info.name, "libdl.so", sizeof(__libdl_info.name)); 239 __libdl_info.flags = FLAG_LINKED | FLAG_NEW_SOINFO; 240 __libdl_info.strtab = ANDROID_LIBDL_STRTAB; 241 __libdl_info.symtab = g_libdl_symtab; 242 __libdl_info.nbucket = sizeof(g_libdl_buckets)/sizeof(unsigned); 243 __libdl_info.nchain = sizeof(g_libdl_chains)/sizeof(unsigned); 244 __libdl_info.bucket = g_libdl_buckets; 245 __libdl_info.chain = g_libdl_chains; 246 __libdl_info.has_DT_SYMBOLIC = true; 247 } 248 249 return &__libdl_info; 250} 251