dlfcn.cpp revision e78deef364d952dd1141a2f3067a12060aaf11e6 
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 <pthread.h>
20#include <stdio.h>
21#include <stdlib.h>
22#include <string.h>
23#include <android/api-level.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_NP;
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 != nullptr) {
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(nullptr);
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,
69                        const android_dlextinfo* extinfo, void* caller_addr) {
70  ScopedPthreadMutexLocker locker(&g_dl_mutex);
71  soinfo* result = do_dlopen(filename, flags, extinfo, caller_addr);
72  if (result == nullptr) {
73    __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
74    return nullptr;
75  }
76  return result;
77}
78
79void* android_dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) {
80  void* caller_addr = __builtin_return_address(0);
81  return dlopen_ext(filename, flags, extinfo, caller_addr);
82}
83
84void* dlopen(const char* filename, int flags) {
85  void* caller_addr = __builtin_return_address(0);
86  return dlopen_ext(filename, flags, nullptr, caller_addr);
87}
88
89extern android_namespace_t* g_anonymous_namespace;
90
91void* dlsym_impl(void* handle, const char* symbol, const char* version, void* caller_addr) {
92  ScopedPthreadMutexLocker locker(&g_dl_mutex);
93  void* result;
94  if (!do_dlsym(handle, symbol, version, caller_addr, &result)) {
95    __bionic_format_dlerror(linker_get_error_buffer(), nullptr);
96    return nullptr;
97  }
98
99  return result;
100}
101
102void* dlsym(void* handle, const char* symbol) {
103  void* caller_addr = __builtin_return_address(0);
104  return dlsym_impl(handle, symbol, nullptr, caller_addr);
105}
106
107void* dlvsym(void* handle, const char* symbol, const char* version) {
108  void* caller_addr = __builtin_return_address(0);
109  return dlsym_impl(handle, symbol, version, caller_addr);
110}
111
112int dladdr(const void* addr, Dl_info* info) {
113  ScopedPthreadMutexLocker locker(&g_dl_mutex);
114  return do_dladdr(addr, info);
115}
116
117int dlclose(void* handle) {
118  ScopedPthreadMutexLocker locker(&g_dl_mutex);
119  do_dlclose(reinterpret_cast<soinfo*>(handle));
120  // dlclose has no defined errors.
121  return 0;
122}
123
124int dl_iterate_phdr(int (*cb)(dl_phdr_info* info, size_t size, void* data), void* data) {
125  ScopedPthreadMutexLocker locker(&g_dl_mutex);
126  return do_dl_iterate_phdr(cb, data);
127}
128
129void android_set_application_target_sdk_version(uint32_t target) {
130  // lock to avoid modification in the middle of dlopen.
131  ScopedPthreadMutexLocker locker(&g_dl_mutex);
132  set_application_target_sdk_version(target);
133}
134
135uint32_t android_get_application_target_sdk_version() {
136  return get_application_target_sdk_version();
137}
138
139bool android_init_namespaces(const char* public_ns_sonames,
140                             const char* anon_ns_library_path) {
141  ScopedPthreadMutexLocker locker(&g_dl_mutex);
142  bool success = init_namespaces(public_ns_sonames, anon_ns_library_path);
143  if (!success) {
144    __bionic_format_dlerror("android_init_namespaces failed", linker_get_error_buffer());
145  }
146
147  return success;
148}
149
150android_namespace_t* android_create_namespace(const char* name, const char* ld_library_path,
151                                              const char* default_library_path, uint64_t type,
152                                              const char* permitted_when_isolated_path) {
153  void* caller_addr = __builtin_return_address(0);
154  ScopedPthreadMutexLocker locker(&g_dl_mutex);
155
156  android_namespace_t* result = create_namespace(caller_addr, name, ld_library_path,
157                                                 default_library_path, type,
158                                                 permitted_when_isolated_path);
159
160  if (result == nullptr) {
161    __bionic_format_dlerror("android_create_namespace failed", linker_get_error_buffer());
162  }
163
164  return result;
165}
166
167// name_offset: starting index of the name in libdl_info.strtab
168#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
169    { name_offset, \
170      reinterpret_cast<Elf32_Addr>(value), \
171      /* st_size */ 0, \
172      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
173      /* st_other */ 0, \
174      shndx, \
175    }
176
177#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
178    { name_offset, \
179      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
180      /* st_other */ 0, \
181      shndx, \
182      reinterpret_cast<Elf64_Addr>(value), \
183      /* st_size */ 0, \
184    }
185
186static const char ANDROID_LIBDL_STRTAB[] =
187  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 99999
188  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 56789
189    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_it"
190  // 00000000001 1111111112222222222 3333333333444444444455555555556666666666777 777777788888888889999999999
191  // 01234567890 1234567890123456789 0123456789012345678901234567890123456789012 345678901234567890123456789
192    "erate_phdr\0android_dlopen_ext\0android_set_application_target_sdk_version\0android_get_application_tar"
193  // 0000000000111111 111122222222223333333333 4444444444555555555566666 6666677
194  // 0123456789012345 678901234567890123456789 0123456789012345678901234 5678901
195    "get_sdk_version\0android_init_namespaces\0android_create_namespace\0dlvsym\0"
196#if defined(__arm__)
197  // 272
198    "dl_unwind_find_exidx\0"
199#endif
200    ;
201
202static ElfW(Sym) g_libdl_symtab[] = {
203  // Total length of libdl_info.strtab, including trailing 0.
204  // This is actually the STH_UNDEF entry. Technically, it's
205  // supposed to have st_name == 0, but instead, it points to an index
206  // in the strtab with a \0 to make iterating through the symtab easier.
207  ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, nullptr, 0),
208  ELFW(SYM_INITIALIZER)(  0, &dlopen, 1),
209  ELFW(SYM_INITIALIZER)(  7, &dlclose, 1),
210  ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
211  ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
212  ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
213  ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
214  ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
215  ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
216  ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1),
217  ELFW(SYM_INITIALIZER)(130, &android_set_application_target_sdk_version, 1),
218  ELFW(SYM_INITIALIZER)(173, &android_get_application_target_sdk_version, 1),
219  ELFW(SYM_INITIALIZER)(216, &android_init_namespaces, 1),
220  ELFW(SYM_INITIALIZER)(240, &android_create_namespace, 1),
221  ELFW(SYM_INITIALIZER)(265, &dlvsym, 1),
222#if defined(__arm__)
223  ELFW(SYM_INITIALIZER)(272, &dl_unwind_find_exidx, 1),
224#endif
225};
226
227// Fake out a hash table with a single bucket.
228//
229// A search of the hash table will look through g_libdl_symtab starting with index 1, then
230// use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to
231// walk through every element in g_libdl_symtab, and then end with 0 (sentinel value).
232//
233// That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number
234// of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not
235// a real symbol). (See soinfo_elf_lookup().)
236//
237// Note that adding any new symbols here requires stubbing them out in libdl.
238static unsigned g_libdl_buckets[1] = { 1 };
239#if defined(__arm__)
240static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0 };
241#else
242static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 0 };
243#endif
244
245static uint8_t __libdl_info_buf[sizeof(soinfo)] __attribute__((aligned(8)));
246static soinfo* __libdl_info = nullptr;
247
248extern android_namespace_t g_default_namespace;
249
250// This is used by the dynamic linker. Every process gets these symbols for free.
251soinfo* get_libdl_info() {
252  if (__libdl_info == nullptr) {
253    __libdl_info = new (__libdl_info_buf) soinfo(&g_default_namespace, "libdl.so", nullptr, 0, RTLD_GLOBAL);
254    __libdl_info->flags_ |= FLAG_LINKED;
255    __libdl_info->strtab_ = ANDROID_LIBDL_STRTAB;
256    __libdl_info->symtab_ = g_libdl_symtab;
257    __libdl_info->nbucket_ = sizeof(g_libdl_buckets)/sizeof(unsigned);
258    __libdl_info->nchain_ = sizeof(g_libdl_chains)/sizeof(unsigned);
259    __libdl_info->bucket_ = g_libdl_buckets;
260    __libdl_info->chain_ = g_libdl_chains;
261    __libdl_info->ref_count_ = 1;
262    __libdl_info->strtab_size_ = sizeof(ANDROID_LIBDL_STRTAB);
263    __libdl_info->local_group_root_ = __libdl_info;
264    __libdl_info->soname_ = "libdl.so";
265    __libdl_info->target_sdk_version_ = __ANDROID_API__;
266#if defined(__work_around_b_24465209__)
267    strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_));
268#endif
269  }
270
271  return __libdl_info;
272}
273