dlfcn.cpp revision e66190d2a97a713ae4b4786e60ca3d67ab8aa192
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 31static pthread_mutex_t gDlMutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER; 32 33static 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 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* dlopen(const char* filename, int flags) { 59 ScopedPthreadMutexLocker locker(&gDlMutex); 60 soinfo* result = do_dlopen(filename, flags); 61 if (result == NULL) { 62 __bionic_format_dlerror("dlopen failed", linker_get_error()); 63 return NULL; 64 } 65 return result; 66} 67 68void* dlsym(void* handle, const char* symbol) { 69 ScopedPthreadMutexLocker locker(&gDlMutex); 70 71 if (handle == NULL) { 72 __bionic_format_dlerror("dlsym library handle is null", NULL); 73 return NULL; 74 } 75 if (symbol == NULL) { 76 __bionic_format_dlerror("dlsym symbol name is null", NULL); 77 return NULL; 78 } 79 80 soinfo* found = NULL; 81 Elf32_Sym* sym = NULL; 82 if (handle == RTLD_DEFAULT) { 83 sym = lookup(symbol, &found, NULL); 84 } else if (handle == RTLD_NEXT) { 85 void* ret_addr = __builtin_return_address(0); 86 soinfo* si = find_containing_library(ret_addr); 87 88 sym = NULL; 89 if (si && si->next) { 90 sym = lookup(symbol, &found, si->next); 91 } 92 } else { 93 found = (soinfo*) handle; 94 sym = soinfo_lookup(found, symbol); 95 } 96 97 if (sym != NULL) { 98 unsigned bind = ELF32_ST_BIND(sym->st_info); 99 100 if (bind == STB_GLOBAL && sym->st_shndx != 0) { 101 unsigned ret = sym->st_value + found->load_bias; 102 return (void*) ret; 103 } 104 105 __bionic_format_dlerror("symbol found but not global", symbol); 106 return NULL; 107 } else { 108 __bionic_format_dlerror("undefined symbol", symbol); 109 return NULL; 110 } 111} 112 113int dladdr(const void* addr, Dl_info* info) { 114 ScopedPthreadMutexLocker locker(&gDlMutex); 115 116 // Determine if this address can be found in any library currently mapped. 117 soinfo* si = find_containing_library(addr); 118 if (si == NULL) { 119 return 0; 120 } 121 122 memset(info, 0, sizeof(Dl_info)); 123 124 info->dli_fname = si->name; 125 // Address at which the shared object is loaded. 126 info->dli_fbase = (void*) si->base; 127 128 // Determine if any symbol in the library contains the specified address. 129 Elf32_Sym *sym = soinfo_find_symbol(si, addr); 130 if (sym != NULL) { 131 info->dli_sname = si->strtab + sym->st_name; 132 info->dli_saddr = (void*)(si->load_bias + sym->st_value); 133 } 134 135 return 1; 136} 137 138int dlclose(void* handle) { 139 ScopedPthreadMutexLocker locker(&gDlMutex); 140 return do_dlclose(reinterpret_cast<soinfo*>(handle)); 141} 142 143#if defined(ANDROID_ARM_LINKER) 144// 0000000 00011111 111112 22222222 2333333 333344444444445555555 145// 0123456 78901234 567890 12345678 9012345 678901234567890123456 146#define ANDROID_LIBDL_STRTAB \ 147 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0dl_unwind_find_exidx\0" 148 149#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 150// 0000000 00011111 111112 22222222 2333333 3333444444444455 151// 0123456 78901234 567890 12345678 9012345 6789012345678901 152#define ANDROID_LIBDL_STRTAB \ 153 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0dl_iterate_phdr\0" 154#else 155#error Unsupported architecture. Only ARM, MIPS, and x86 are presently supported. 156#endif 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 167static Elf32_Sym gLibDlSymtab[] = { 168 // Total length of libdl_info.strtab, including trailing 0. 169 // This is actually the STH_UNDEF entry. Technically, it's 170 // supposed to have st_name == 0, but instead, it points to an index 171 // in the strtab with a \0 to make iterating through the symtab easier. 172 ELF32_SYM_INITIALIZER(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0), 173 ELF32_SYM_INITIALIZER( 0, &dlopen, 1), 174 ELF32_SYM_INITIALIZER( 7, &dlclose, 1), 175 ELF32_SYM_INITIALIZER(15, &dlsym, 1), 176 ELF32_SYM_INITIALIZER(21, &dlerror, 1), 177 ELF32_SYM_INITIALIZER(29, &dladdr, 1), 178#if defined(ANDROID_ARM_LINKER) 179 ELF32_SYM_INITIALIZER(36, &dl_unwind_find_exidx, 1), 180#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 181 ELF32_SYM_INITIALIZER(36, &dl_iterate_phdr, 1), 182#endif 183}; 184 185// Fake out a hash table with a single bucket. 186// A search of the hash table will look through 187// gLibDlSymtab starting with index [1], then 188// use gLibDlChains to find the next index to 189// look at. gLibDlChains should be set up to 190// walk through every element in gLibDlSymtab, 191// and then end with 0 (sentinel value). 192// 193// That is, gLibDlChains should look like 194// { 0, 2, 3, ... N, 0 } where N is the number 195// of actual symbols, or nelems(gLibDlSymtab)-1 196// (since the first element of gLibDlSymtab is not 197// a real symbol). 198// 199// (see soinfo_elf_lookup()) 200// 201// Note that adding any new symbols here requires 202// stubbing them out in libdl. 203static unsigned gLibDlBuckets[1] = { 1 }; 204static unsigned gLibDlChains[7] = { 0, 2, 3, 4, 5, 6, 0 }; 205 206// This is used by the dynamic linker. Every process gets these symbols for free. 207soinfo libdl_info = { 208 "libdl.so", 209 210 phdr: 0, phnum: 0, 211 entry: 0, base: 0, size: 0, 212 unused: 0, dynamic: 0, unused2: 0, unused3: 0, 213 next: 0, 214 215 flags: FLAG_LINKED, 216 217 strtab: ANDROID_LIBDL_STRTAB, 218 symtab: gLibDlSymtab, 219 220 nbucket: 1, 221 nchain: 7, 222 bucket: gLibDlBuckets, 223 chain: gLibDlChains, 224 225 plt_got: 0, plt_rel: 0, plt_rel_count: 0, rel: 0, rel_count: 0, 226 preinit_array: 0, preinit_array_count: 0, init_array: 0, init_array_count: 0, 227 fini_array: 0, fini_array_count: 0, init_func: 0, fini_func: 0, 228 229#if defined(ANDROID_ARM_LINKER) 230 ARM_exidx: 0, ARM_exidx_count: 0, 231#elif defined(ANDROID_MIPS_LINKER) 232 mips_symtabno: 0, mips_local_gotno: 0, mips_gotsym: 0, 233#endif 234 235 refcount: 0, 236 { l_addr: 0, l_name: 0, l_ld: 0, l_next: 0, l_prev: 0, }, 237 constructors_called: false, 238 load_bias: 0, 239 has_text_relocations: false, 240 has_DT_SYMBOLIC: true, 241}; 242