dlfcn.cpp revision 1a586293400d0e1d73e6eb82f7dfe9d2d9ed3c4b 
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  if (handle == RTLD_DEFAULT || handle == (void*)0xffffffffL) {
104    sym = dlsym_linear_lookup(symbol, &found, NULL);
105  } else if (handle == RTLD_NEXT || handle == (void*)0xfffffffeL) {
106    void* caller_addr = __builtin_return_address(0);
107    soinfo* si = find_containing_library(caller_addr);
108
109    sym = NULL;
110    if (si && si->next) {
111      sym = dlsym_linear_lookup(symbol, &found, si->next);
112    }
113  } else {
114    found = reinterpret_cast<soinfo*>(handle);
115    sym = dlsym_handle_lookup(found, symbol);
116  }
117
118  if (sym != NULL) {
119    unsigned bind = ELF_ST_BIND(sym->st_info);
120
121    if (bind == STB_GLOBAL && sym->st_shndx != 0) {
122      return reinterpret_cast<void*>(sym->st_value + found->load_bias);
123    }
124
125    __bionic_format_dlerror("symbol found but not global", symbol);
126    return NULL;
127  } else {
128    __bionic_format_dlerror("undefined symbol", symbol);
129    return NULL;
130  }
131}
132
133int dladdr(const void* addr, Dl_info* info) {
134  ScopedPthreadMutexLocker locker(&g_dl_mutex);
135
136  // Determine if this address can be found in any library currently mapped.
137  soinfo* si = find_containing_library(addr);
138  if (si == NULL) {
139    return 0;
140  }
141
142  memset(info, 0, sizeof(Dl_info));
143
144  info->dli_fname = si->name;
145  // Address at which the shared object is loaded.
146  info->dli_fbase = reinterpret_cast<void*>(si->base);
147
148  // Determine if any symbol in the library contains the specified address.
149  ElfW(Sym)* sym = dladdr_find_symbol(si, addr);
150  if (sym != NULL) {
151    info->dli_sname = si->strtab + sym->st_name;
152    info->dli_saddr = reinterpret_cast<void*>(si->load_bias + sym->st_value);
153  }
154
155  return 1;
156}
157
158int dlclose(void* handle) {
159  ScopedPthreadMutexLocker locker(&g_dl_mutex);
160  do_dlclose(reinterpret_cast<soinfo*>(handle));
161  // dlclose has no defined errors.
162  return 0;
163}
164
165// name_offset: starting index of the name in libdl_info.strtab
166#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
167    { name_offset, \
168      reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
169      /* st_size */ 0, \
170      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
171      /* st_other */ 0, \
172      shndx, \
173    }
174
175#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
176    { name_offset, \
177      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
178      /* st_other */ 0, \
179      shndx, \
180      reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
181      /* st_size */ 0, \
182    }
183
184#if defined(__arm__)
185  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222 333333333344444444445
186  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789 012345678901234567890
187#  define ANDROID_LIBDL_STRTAB \
188    "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"
189#elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
190  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222
191  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789
192#  define ANDROID_LIBDL_STRTAB \
193    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0android_dlopen_ext\0"
194#else
195#  error Unsupported architecture. Only arm, arm64, mips, mips64, x86 and x86_64 are presently supported.
196#endif
197
198static ElfW(Sym) g_libdl_symtab[] = {
199  // Total length of libdl_info.strtab, including trailing 0.
200  // This is actually the STH_UNDEF entry. Technically, it's
201  // supposed to have st_name == 0, but instead, it points to an index
202  // in the strtab with a \0 to make iterating through the symtab easier.
203  ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
204  ELFW(SYM_INITIALIZER)(  0, &dlopen, 1),
205  ELFW(SYM_INITIALIZER)(  7, &dlclose, 1),
206  ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
207  ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
208  ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
209  ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
210  ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
211  ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
212  ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1),
213#if defined(__arm__)
214  ELFW(SYM_INITIALIZER)(130, &dl_unwind_find_exidx, 1),
215#endif
216};
217
218// Fake out a hash table with a single bucket.
219//
220// A search of the hash table will look through g_libdl_symtab starting with index 1, then
221// use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to
222// walk through every element in g_libdl_symtab, and then end with 0 (sentinel value).
223//
224// That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number
225// of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not
226// a real symbol). (See soinfo_elf_lookup().)
227//
228// Note that adding any new symbols here requires stubbing them out in libdl.
229static unsigned g_libdl_buckets[1] = { 1 };
230#if defined(__arm__)
231static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0 };
232#else
233static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
234#endif
235
236// Defined as global because we do not yet have access
237// to synchronization functions __cxa_guard_* needed
238// to define statics inside functions.
239static soinfo __libdl_info;
240
241// This is used by the dynamic linker. Every process gets these symbols for free.
242soinfo* get_libdl_info() {
243  if (__libdl_info.name[0] == '\0') {
244    // initialize
245    strncpy(__libdl_info.name, "libdl.so", sizeof(__libdl_info.name));
246    __libdl_info.flags = FLAG_LINKED | FLAG_NEW_SOINFO;
247    __libdl_info.strtab = ANDROID_LIBDL_STRTAB;
248    __libdl_info.symtab = g_libdl_symtab;
249    __libdl_info.nbucket = sizeof(g_libdl_buckets)/sizeof(unsigned);
250    __libdl_info.nchain = sizeof(g_libdl_chains)/sizeof(unsigned);
251    __libdl_info.bucket = g_libdl_buckets;
252    __libdl_info.chain = g_libdl_chains;
253    __libdl_info.has_DT_SYMBOLIC = true;
254  }
255
256  return &__libdl_info;
257}
258