dlfcn.cpp revision 1b1966d9448e979d1503a3d8843708bfa8880dc6 
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  void* caller_addr = __builtin_return_address(0);
104  soinfo* caller_si = find_containing_library(caller_addr);
105
106  if (handle == RTLD_DEFAULT) {
107    sym = dlsym_linear_lookup(symbol, &found, NULL, caller_si);
108  } else if (handle == RTLD_NEXT) {
109    sym = NULL;
110    if (caller_si && caller_si->next) {
111      sym = dlsym_linear_lookup(symbol, &found, caller_si->next, caller_si);
112    }
113  } else {
114    found = reinterpret_cast<soinfo*>(handle);
115    sym = dlsym_handle_lookup(found, symbol, caller_si);
116  }
117
118  if (sym != NULL && sym->st_shndx != 0) {
119    return reinterpret_cast<void*>(sym->st_value + found->load_bias);
120  } else {
121    __bionic_format_dlerror("undefined symbol", symbol);
122    return NULL;
123  }
124}
125
126int dladdr(const void* addr, Dl_info* info) {
127  ScopedPthreadMutexLocker locker(&g_dl_mutex);
128
129  // Determine if this address can be found in any library currently mapped.
130  soinfo* si = find_containing_library(addr);
131  if (si == NULL) {
132    return 0;
133  }
134
135  memset(info, 0, sizeof(Dl_info));
136
137  info->dli_fname = si->name;
138  // Address at which the shared object is loaded.
139  info->dli_fbase = reinterpret_cast<void*>(si->base);
140
141  // Determine if any symbol in the library contains the specified address.
142  ElfW(Sym)* sym = dladdr_find_symbol(si, addr);
143  if (sym != NULL) {
144    info->dli_sname = si->strtab + sym->st_name;
145    info->dli_saddr = reinterpret_cast<void*>(si->load_bias + sym->st_value);
146  }
147
148  return 1;
149}
150
151int dlclose(void* handle) {
152  ScopedPthreadMutexLocker locker(&g_dl_mutex);
153  do_dlclose(reinterpret_cast<soinfo*>(handle));
154  // dlclose has no defined errors.
155  return 0;
156}
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    }
167
168#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
169    { name_offset, \
170      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
171      /* st_other */ 0, \
172      shndx, \
173      reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
174      /* st_size */ 0, \
175    }
176
177#if defined(__arm__)
178  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222 333333333344444444445
179  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789 012345678901234567890
180#  define ANDROID_LIBDL_STRTAB \
181    "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"
182#elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
183  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222
184  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789
185#  define ANDROID_LIBDL_STRTAB \
186    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0android_dlopen_ext\0"
187#else
188#  error Unsupported architecture. Only arm, arm64, mips, mips64, x86 and x86_64 are presently supported.
189#endif
190
191static ElfW(Sym) g_libdl_symtab[] = {
192  // Total length of libdl_info.strtab, including trailing 0.
193  // This is actually the STH_UNDEF entry. Technically, it's
194  // supposed to have st_name == 0, but instead, it points to an index
195  // in the strtab with a \0 to make iterating through the symtab easier.
196  ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
197  ELFW(SYM_INITIALIZER)(  0, &dlopen, 1),
198  ELFW(SYM_INITIALIZER)(  7, &dlclose, 1),
199  ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
200  ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
201  ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
202  ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
203  ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
204  ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
205  ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1),
206#if defined(__arm__)
207  ELFW(SYM_INITIALIZER)(130, &dl_unwind_find_exidx, 1),
208#endif
209};
210
211// Fake out a hash table with a single bucket.
212//
213// A search of the hash table will look through g_libdl_symtab starting with index 1, then
214// use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to
215// walk through every element in g_libdl_symtab, and then end with 0 (sentinel value).
216//
217// That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number
218// of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not
219// a real symbol). (See soinfo_elf_lookup().)
220//
221// Note that adding any new symbols here requires stubbing them out in libdl.
222static unsigned g_libdl_buckets[1] = { 1 };
223#if defined(__arm__)
224static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0 };
225#else
226static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
227#endif
228
229// Defined as global because we do not yet have access
230// to synchronization functions __cxa_guard_* needed
231// to define statics inside functions.
232static soinfo __libdl_info;
233
234// This is used by the dynamic linker. Every process gets these symbols for free.
235soinfo* get_libdl_info() {
236  if (__libdl_info.name[0] == '\0') {
237    // initialize
238    strncpy(__libdl_info.name, "libdl.so", sizeof(__libdl_info.name));
239    __libdl_info.flags = FLAG_LINKED | FLAG_NEW_SOINFO;
240    __libdl_info.strtab = ANDROID_LIBDL_STRTAB;
241    __libdl_info.symtab = g_libdl_symtab;
242    __libdl_info.nbucket = sizeof(g_libdl_buckets)/sizeof(unsigned);
243    __libdl_info.nchain = sizeof(g_libdl_chains)/sizeof(unsigned);
244    __libdl_info.bucket = g_libdl_buckets;
245    __libdl_info.chain = g_libdl_chains;
246    __libdl_info.has_DT_SYMBOLIC = true;
247  }
248
249  return &__libdl_info;
250}
251