dlfcn.cpp revision c00f2cb587630d5e954c7f548749f1e3170b3cb1 
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 android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
59  ScopedPthreadMutexLocker locker(&gDlMutex);
60  do_android_update_LD_LIBRARY_PATH(ld_library_path);
61}
62
63void* dlopen(const char* filename, int flags) {
64  ScopedPthreadMutexLocker locker(&gDlMutex);
65  soinfo* result = do_dlopen(filename, flags);
66  if (result == NULL) {
67    __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
68    return NULL;
69  }
70  return result;
71}
72
73void* dlsym(void* handle, const char* symbol) {
74  ScopedPthreadMutexLocker locker(&gDlMutex);
75
76  if (handle == NULL) {
77    __bionic_format_dlerror("dlsym library handle is null", NULL);
78    return NULL;
79  }
80  if (symbol == NULL) {
81    __bionic_format_dlerror("dlsym symbol name is null", NULL);
82    return NULL;
83  }
84
85  soinfo* found = NULL;
86  Elf_Sym* sym = NULL;
87  if (handle == RTLD_DEFAULT) {
88    sym = dlsym_linear_lookup(symbol, &found, NULL);
89  } else if (handle == RTLD_NEXT) {
90    void* ret_addr = __builtin_return_address(0);
91    soinfo* si = find_containing_library(ret_addr);
92
93    sym = NULL;
94    if (si && si->next) {
95      sym = dlsym_linear_lookup(symbol, &found, si->next);
96    }
97  } else {
98    found = reinterpret_cast<soinfo*>(handle);
99    sym = dlsym_handle_lookup(found, symbol);
100  }
101
102  if (sym != NULL) {
103    unsigned bind = ELF_ST_BIND(sym->st_info);
104
105    if (bind == STB_GLOBAL && sym->st_shndx != 0) {
106      return reinterpret_cast<void*>(sym->st_value + found->load_bias);
107    }
108
109    __bionic_format_dlerror("symbol found but not global", symbol);
110    return NULL;
111  } else {
112    __bionic_format_dlerror("undefined symbol", symbol);
113    return NULL;
114  }
115}
116
117int dladdr(const void* addr, Dl_info* info) {
118  ScopedPthreadMutexLocker locker(&gDlMutex);
119
120  // Determine if this address can be found in any library currently mapped.
121  soinfo* si = find_containing_library(addr);
122  if (si == NULL) {
123    return 0;
124  }
125
126  memset(info, 0, sizeof(Dl_info));
127
128  info->dli_fname = si->name;
129  // Address at which the shared object is loaded.
130  info->dli_fbase = (void*) si->base;
131
132  // Determine if any symbol in the library contains the specified address.
133  Elf_Sym *sym = dladdr_find_symbol(si, addr);
134  if (sym != NULL) {
135    info->dli_sname = si->strtab + sym->st_name;
136    info->dli_saddr = (void*)(si->load_bias + sym->st_value);
137  }
138
139  return 1;
140}
141
142int dlclose(void* handle) {
143  ScopedPthreadMutexLocker locker(&gDlMutex);
144  return do_dlclose(reinterpret_cast<soinfo*>(handle));
145}
146
147#if defined(ANDROID_ARM_LINKER)
148//   0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888 8888888
149//   0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012 3456789
150#define ANDROID_LIBDL_STRTAB \
151    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0dl_iterate_phdr\0dl_unwind_find_exidx\0"
152#elif defined(ANDROID_MIPS_LINKER) || defined(ANDROID_X86_LINKER) || defined(ANDROID_X86_64_LINKER)
153//   0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667
154//   0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890
155#define ANDROID_LIBDL_STRTAB \
156    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0dl_iterate_phdr\0"
157#else
158#error Unsupported architecture. Only ARM, MIPS, x86, and x86_64 are presently supported.
159#endif
160
161// name_offset: starting index of the name in libdl_info.strtab
162#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
163    { name_offset, \
164      reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
165      /* st_size */ 0, \
166      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
167      /* st_other */ 0, \
168      shndx, \
169    }
170
171#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
172    { name_offset, \
173      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
174      /* st_other */ 0, \
175      shndx, \
176      reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
177      /* st_size */ 0, \
178    }
179
180#if defined(__LP64__)
181#  define ELF_SYM_INITIALIZER ELF64_SYM_INITIALIZER
182#else
183#  define ELF_SYM_INITIALIZER ELF32_SYM_INITIALIZER
184#endif
185
186static Elf_Sym gLibDlSymtab[] = {
187  // Total length of libdl_info.strtab, including trailing 0.
188  // This is actually the STH_UNDEF entry. Technically, it's
189  // supposed to have st_name == 0, but instead, it points to an index
190  // in the strtab with a \0 to make iterating through the symtab easier.
191  ELF_SYM_INITIALIZER(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
192  ELF_SYM_INITIALIZER( 0, &dlopen, 1),
193  ELF_SYM_INITIALIZER( 7, &dlclose, 1),
194  ELF_SYM_INITIALIZER(15, &dlsym, 1),
195  ELF_SYM_INITIALIZER(21, &dlerror, 1),
196  ELF_SYM_INITIALIZER(29, &dladdr, 1),
197  ELF_SYM_INITIALIZER(36, &android_update_LD_LIBRARY_PATH, 1),
198  ELF_SYM_INITIALIZER(67, &dl_iterate_phdr, 1),
199#if defined(ANDROID_ARM_LINKER)
200  ELF_SYM_INITIALIZER(83, &dl_unwind_find_exidx, 1),
201#endif
202};
203
204// Fake out a hash table with a single bucket.
205// A search of the hash table will look through
206// gLibDlSymtab starting with index [1], then
207// use gLibDlChains to find the next index to
208// look at.  gLibDlChains should be set up to
209// walk through every element in gLibDlSymtab,
210// and then end with 0 (sentinel value).
211//
212// That is, gLibDlChains should look like
213// { 0, 2, 3, ... N, 0 } where N is the number
214// of actual symbols, or nelems(gLibDlSymtab)-1
215// (since the first element of gLibDlSymtab is not
216// a real symbol).
217//
218// (see soinfo_elf_lookup())
219//
220// Note that adding any new symbols here requires
221// stubbing them out in libdl.
222static unsigned gLibDlBuckets[1] = { 1 };
223#if defined(ANDROID_ARM_LINKER)
224static unsigned gLibDlChains[9] = { 0, 2, 3, 4, 5, 6, 7, 8, 0 };
225#else
226static unsigned gLibDlChains[8] = { 0, 2, 3, 4, 5, 6, 7, 0 };
227#endif
228
229// This is used by the dynamic linker. Every process gets these symbols for free.
230soinfo libdl_info = {
231    "libdl.so",
232
233    phdr: 0,
234    phnum: 0,
235    entry: 0,
236    base: 0,
237    size: 0,
238#if !defined(__LP64__)
239    unused1: 0,
240#endif
241    dynamic: 0,
242#if !defined(__LP64__)
243    unused2: 0, unused3: 0,
244#endif
245    next: 0,
246
247    flags: FLAG_LINKED,
248
249    strtab: ANDROID_LIBDL_STRTAB,
250    symtab: gLibDlSymtab,
251
252    nbucket: sizeof(gLibDlBuckets)/sizeof(unsigned),
253    nchain: sizeof(gLibDlChains)/sizeof(unsigned),
254    bucket: gLibDlBuckets,
255    chain: gLibDlChains,
256
257#if defined(ANDROID_X86_64_LINKER)
258    plt_rela: 0,
259    plt_rela_count: 0,
260    rela: 0,
261    rela_count: 0,
262#else
263    plt_got: 0,
264    plt_rel: 0,
265    plt_rel_count: 0,
266    rel: 0,
267    rel_count: 0,
268#endif
269
270    preinit_array: 0,
271    preinit_array_count: 0,
272
273    init_array: 0,
274    init_array_count: 0,
275
276    fini_array: 0,
277    fini_array_count: 0,
278
279    init_func: 0,
280    fini_func: 0,
281
282#if defined(ANDROID_ARM_LINKER)
283    ARM_exidx: 0,
284    ARM_exidx_count: 0,
285#elif defined(ANDROID_MIPS_LINKER)
286    mips_symtabno: 0,
287    mips_local_gotno: 0,
288    mips_gotsym: 0,
289#endif
290
291    ref_count: 0,
292    { l_addr: 0, l_name: 0, l_ld: 0, l_next: 0, l_prev: 0, },
293    constructors_called: false,
294    load_bias: 0,
295    has_text_relocations: false,
296    has_DT_SYMBOLIC: true,
297};
298