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
161int dl_iterate_phdr(int (*cb)(dl_phdr_info* info, size_t size, void* data), void* data) {
162  ScopedPthreadMutexLocker locker(&g_dl_mutex);
163  return do_dl_iterate_phdr(cb, data);
164}
165
166void android_set_application_target_sdk_version(uint32_t target) {
167  // lock to avoid modification in the middle of dlopen.
168  ScopedPthreadMutexLocker locker(&g_dl_mutex);
169  set_application_target_sdk_version(target);
170}
171
172uint32_t android_get_application_target_sdk_version() {
173  return get_application_target_sdk_version();
174}
175
176// name_offset: starting index of the name in libdl_info.strtab
177#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
178    { name_offset, \
179      reinterpret_cast<Elf32_Addr>(value), \
180      /* st_size */ 0, \
181      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
182      /* st_other */ 0, \
183      shndx, \
184    }
185
186#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
187    { name_offset, \
188      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
189      /* st_other */ 0, \
190      shndx, \
191      reinterpret_cast<Elf64_Addr>(value), \
192      /* st_size */ 0, \
193    }
194
195static const char ANDROID_LIBDL_STRTAB[] =
196  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 99999
197  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 56789
198    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_it"
199  // 00000000001 1111111112222222222 3333333333444444444455555555556666666666777 777777788888888889999999999
200  // 01234567890 1234567890123456789 0123456789012345678901234567890123456789012 345678901234567890123456789
201    "erate_phdr\0android_dlopen_ext\0android_set_application_target_sdk_version\0android_get_application_tar"
202  // 0000000000111111
203  // 0123456789012345
204    "get_sdk_version\0"
205#if defined(__arm__)
206  // 216
207    "dl_unwind_find_exidx\0"
208#endif
209    ;
210
211static ElfW(Sym) g_libdl_symtab[] = {
212  // Total length of libdl_info.strtab, including trailing 0.
213  // This is actually the STH_UNDEF entry. Technically, it's
214  // supposed to have st_name == 0, but instead, it points to an index
215  // in the strtab with a \0 to make iterating through the symtab easier.
216  ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, nullptr, 0),
217  ELFW(SYM_INITIALIZER)(  0, &dlopen, 1),
218  ELFW(SYM_INITIALIZER)(  7, &dlclose, 1),
219  ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
220  ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
221  ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
222  ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
223  ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
224  ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
225  ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1),
226  ELFW(SYM_INITIALIZER)(130, &android_set_application_target_sdk_version, 1),
227  ELFW(SYM_INITIALIZER)(173, &android_get_application_target_sdk_version, 1),
228#if defined(__arm__)
229  ELFW(SYM_INITIALIZER)(216, &dl_unwind_find_exidx, 1),
230#endif
231};
232
233// Fake out a hash table with a single bucket.
234//
235// A search of the hash table will look through g_libdl_symtab starting with index 1, then
236// use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to
237// walk through every element in g_libdl_symtab, and then end with 0 (sentinel value).
238//
239// That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number
240// of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not
241// a real symbol). (See soinfo_elf_lookup().)
242//
243// Note that adding any new symbols here requires stubbing them out in libdl.
244static unsigned g_libdl_buckets[1] = { 1 };
245#if defined(__arm__)
246static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0 };
247#else
248static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 0 };
249#endif
250
251static uint8_t __libdl_info_buf[sizeof(soinfo)] __attribute__((aligned(8)));
252static soinfo* __libdl_info = nullptr;
253
254// This is used by the dynamic linker. Every process gets these symbols for free.
255soinfo* get_libdl_info() {
256  if (__libdl_info == nullptr) {
257    __libdl_info = new (__libdl_info_buf) soinfo("libdl.so", nullptr, 0, RTLD_GLOBAL);
258    __libdl_info->flags_ |= FLAG_LINKED;
259    __libdl_info->strtab_ = ANDROID_LIBDL_STRTAB;
260    __libdl_info->symtab_ = g_libdl_symtab;
261    __libdl_info->nbucket_ = sizeof(g_libdl_buckets)/sizeof(unsigned);
262    __libdl_info->nchain_ = sizeof(g_libdl_chains)/sizeof(unsigned);
263    __libdl_info->bucket_ = g_libdl_buckets;
264    __libdl_info->chain_ = g_libdl_chains;
265    __libdl_info->ref_count_ = 1;
266    __libdl_info->strtab_size_ = sizeof(ANDROID_LIBDL_STRTAB);
267    __libdl_info->local_group_root_ = __libdl_info;
268    __libdl_info->soname_ = "libdl.so";
269    __libdl_info->target_sdk_version_ = __ANDROID_API__;
270#if defined(__arm__)
271    strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_));
272#endif
273  }
274
275  return __libdl_info;
276}
277