dlfcn.cpp revision 5419b9474753d25dff947c7740532f86d130c0be
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 flag) { 59 ScopedPthreadMutexLocker locker(&gDlMutex); 60 soinfo* result = find_library(filename); 61 if (result == NULL) { 62 __bionic_format_dlerror("dlopen failed", linker_get_error()); 63 return NULL; 64 } 65 soinfo_call_constructors(result); 66 result->refcount++; 67 return result; 68} 69 70void* dlsym(void* handle, const char* symbol) { 71 ScopedPthreadMutexLocker locker(&gDlMutex); 72 73 if (handle == NULL) { 74 __bionic_format_dlerror("dlsym library handle is null", NULL); 75 return NULL; 76 } 77 if (symbol == NULL) { 78 __bionic_format_dlerror("dlsym symbol name is null", NULL); 79 return NULL; 80 } 81 82 soinfo* found = NULL; 83 Elf32_Sym* sym = NULL; 84 if (handle == RTLD_DEFAULT) { 85 sym = lookup(symbol, &found, NULL); 86 } else if (handle == RTLD_NEXT) { 87 void* ret_addr = __builtin_return_address(0); 88 soinfo* si = find_containing_library(ret_addr); 89 90 sym = NULL; 91 if (si && si->next) { 92 sym = lookup(symbol, &found, si->next); 93 } 94 } else { 95 found = (soinfo*) handle; 96 sym = soinfo_lookup(found, symbol); 97 } 98 99 if (sym != NULL) { 100 unsigned bind = ELF32_ST_BIND(sym->st_info); 101 102 if (bind == STB_GLOBAL && sym->st_shndx != 0) { 103 unsigned ret = sym->st_value + found->load_bias; 104 return (void*) ret; 105 } 106 107 __bionic_format_dlerror("symbol found but not global", symbol); 108 return NULL; 109 } else { 110 __bionic_format_dlerror("undefined symbol", symbol); 111 return NULL; 112 } 113} 114 115int dladdr(const void* addr, Dl_info* info) { 116 ScopedPthreadMutexLocker locker(&gDlMutex); 117 118 // Determine if this address can be found in any library currently mapped. 119 soinfo* si = find_containing_library(addr); 120 if (si == NULL) { 121 return 0; 122 } 123 124 memset(info, 0, sizeof(Dl_info)); 125 126 info->dli_fname = si->name; 127 // Address at which the shared object is loaded. 128 info->dli_fbase = (void*) si->base; 129 130 // Determine if any symbol in the library contains the specified address. 131 Elf32_Sym *sym = soinfo_find_symbol(si, addr); 132 if (sym != NULL) { 133 info->dli_sname = si->strtab + sym->st_name; 134 info->dli_saddr = (void*)(si->load_bias + sym->st_value); 135 } 136 137 return 1; 138} 139 140int dlclose(void* handle) { 141 ScopedPthreadMutexLocker locker(&gDlMutex); 142 return soinfo_unload((soinfo*) handle); 143} 144 145#if defined(ANDROID_ARM_LINKER) 146// 0000000 00011111 111112 22222222 2333333 333344444444445555555 147// 0123456 78901234 567890 12345678 9012345 678901234567890123456 148#define ANDROID_LIBDL_STRTAB \ 149 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0dl_unwind_find_exidx\0" 150 151#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 152// 0000000 00011111 111112 22222222 2333333 3333444444444455 153// 0123456 78901234 567890 12345678 9012345 6789012345678901 154#define ANDROID_LIBDL_STRTAB \ 155 "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0dl_iterate_phdr\0" 156#else 157#error Unsupported architecture. Only ARM, MIPS, and x86 are presently supported. 158#endif 159 160// name_offset: starting index of the name in libdl_info.strtab 161#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \ 162 { name_offset, \ 163 reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \ 164 /* st_size */ 0, \ 165 (shndx == 0) ? 0 : (STB_GLOBAL << 4), \ 166 /* st_other */ 0, \ 167 shndx } 168 169static Elf32_Sym gLibDlSymtab[] = { 170 // Total length of libdl_info.strtab, including trailing 0. 171 // This is actually the STH_UNDEF entry. Technically, it's 172 // supposed to have st_name == 0, but instead, it points to an index 173 // in the strtab with a \0 to make iterating through the symtab easier. 174 ELF32_SYM_INITIALIZER(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0), 175 ELF32_SYM_INITIALIZER( 0, &dlopen, 1), 176 ELF32_SYM_INITIALIZER( 7, &dlclose, 1), 177 ELF32_SYM_INITIALIZER(15, &dlsym, 1), 178 ELF32_SYM_INITIALIZER(21, &dlerror, 1), 179 ELF32_SYM_INITIALIZER(29, &dladdr, 1), 180#if defined(ANDROID_ARM_LINKER) 181 ELF32_SYM_INITIALIZER(36, &dl_unwind_find_exidx, 1), 182#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) 183 ELF32_SYM_INITIALIZER(36, &dl_iterate_phdr, 1), 184#endif 185}; 186 187// Fake out a hash table with a single bucket. 188// A search of the hash table will look through 189// gLibDlSymtab starting with index [1], then 190// use gLibDlChains to find the next index to 191// look at. gLibDlChains should be set up to 192// walk through every element in gLibDlSymtab, 193// and then end with 0 (sentinel value). 194// 195// That is, gLibDlChains should look like 196// { 0, 2, 3, ... N, 0 } where N is the number 197// of actual symbols, or nelems(gLibDlSymtab)-1 198// (since the first element of gLibDlSymtab is not 199// a real symbol). 200// 201// (see soinfo_elf_lookup()) 202// 203// Note that adding any new symbols here requires 204// stubbing them out in libdl. 205static unsigned gLibDlBuckets[1] = { 1 }; 206static unsigned gLibDlChains[7] = { 0, 2, 3, 4, 5, 6, 0 }; 207 208// This is used by the dynamic linker. Every process gets these symbols for free. 209soinfo libdl_info = { 210 name: "libdl.so", 211 212 phdr: 0, phnum: 0, 213 entry: 0, base: 0, size: 0, 214 unused: 0, dynamic: 0, unused2: 0, unused3: 0, 215 next: 0, 216 217 flags: FLAG_LINKED, 218 219 strtab: ANDROID_LIBDL_STRTAB, 220 symtab: gLibDlSymtab, 221 222 nbucket: 1, 223 nchain: 7, 224 bucket: gLibDlBuckets, 225 chain: gLibDlChains, 226 227 plt_got: 0, plt_rel: 0, plt_rel_count: 0, rel: 0, rel_count: 0, 228 preinit_array: 0, preinit_array_count: 0, init_array: 0, init_array_count: 0, 229 fini_array: 0, fini_array_count: 0, init_func: 0, fini_func: 0, 230 231#if defined(ANDROID_ARM_LINKER) 232 ARM_exidx: 0, ARM_exidx_count: 0, 233#elif defined(ANDROID_MIPS_LINKER) 234 mips_symtabno: 0, mips_local_gotno: 0, mips_gotsym: 0, 235#endif 236 237 refcount: 0, 238 { l_addr: 0, l_name: 0, l_ld: 0, l_next: 0, l_prev: 0, }, 239 constructors_called: 0, load_bias: 0, has_text_relocations: 0, 240}; 241