dlfcn.cpp revision 012cb4583a5f8564059142bb1900ea3a31e7cfa9 
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 gDlMutex = 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(&gDlMutex);
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(&gDlMutex);
65  do_android_update_LD_LIBRARY_PATH(ld_library_path);
66}
67
68void* android_dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo)
69{
70  ScopedPthreadMutexLocker locker(&gDlMutex);
71  soinfo* result = do_dlopen(filename, flags, extinfo);
72  if (result == NULL) {
73    __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
74    return NULL;
75  }
76  return result;
77}
78
79void* dlopen(const char* filename, int flags) {
80  return android_dlopen_ext(filename, flags, NULL);
81}
82
83void* dlsym(void* handle, const char* symbol) {
84  ScopedPthreadMutexLocker locker(&gDlMutex);
85
86  if (handle == NULL) {
87    __bionic_format_dlerror("dlsym library handle is null", NULL);
88    return NULL;
89  }
90  if (symbol == NULL) {
91    __bionic_format_dlerror("dlsym symbol name is null", NULL);
92    return NULL;
93  }
94
95  soinfo* found = NULL;
96  ElfW(Sym)* sym = NULL;
97  if (handle == RTLD_DEFAULT) {
98    sym = dlsym_linear_lookup(symbol, &found, NULL);
99  } else if (handle == RTLD_NEXT) {
100    void* ret_addr = __builtin_return_address(0);
101    soinfo* si = find_containing_library(ret_addr);
102
103    sym = NULL;
104    if (si && si->next) {
105      sym = dlsym_linear_lookup(symbol, &found, si->next);
106    }
107  } else {
108    found = reinterpret_cast<soinfo*>(handle);
109    sym = dlsym_handle_lookup(found, symbol);
110  }
111
112  if (sym != NULL) {
113    unsigned bind = ELF_ST_BIND(sym->st_info);
114
115    if (bind == STB_GLOBAL && sym->st_shndx != 0) {
116      return reinterpret_cast<void*>(sym->st_value + found->load_bias);
117    }
118
119    __bionic_format_dlerror("symbol found but not global", symbol);
120    return NULL;
121  } else {
122    __bionic_format_dlerror("undefined symbol", symbol);
123    return NULL;
124  }
125}
126
127int dladdr(const void* addr, Dl_info* info) {
128  ScopedPthreadMutexLocker locker(&gDlMutex);
129
130  // Determine if this address can be found in any library currently mapped.
131  soinfo* si = find_containing_library(addr);
132  if (si == NULL) {
133    return 0;
134  }
135
136  memset(info, 0, sizeof(Dl_info));
137
138  info->dli_fname = si->name;
139  // Address at which the shared object is loaded.
140  info->dli_fbase = reinterpret_cast<void*>(si->base);
141
142  // Determine if any symbol in the library contains the specified address.
143  ElfW(Sym)* sym = dladdr_find_symbol(si, addr);
144  if (sym != NULL) {
145    info->dli_sname = si->strtab + sym->st_name;
146    info->dli_saddr = reinterpret_cast<void*>(si->load_bias + sym->st_value);
147  }
148
149  return 1;
150}
151
152int dlclose(void* handle) {
153  ScopedPthreadMutexLocker locker(&gDlMutex);
154  return do_dlclose(reinterpret_cast<soinfo*>(handle));
155}
156
157// name_offset: starting index of the name in libdl_info.strtab
158#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
159    { name_offset, \
160      reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
161      /* st_size */ 0, \
162      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
163      /* st_other */ 0, \
164      shndx, \
165    }
166
167#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
168    { name_offset, \
169      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
170      /* st_other */ 0, \
171      shndx, \
172      reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
173      /* st_size */ 0, \
174    }
175
176#if defined(__arm__)
177  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222 333333333344444444445
178  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789 012345678901234567890
179#  define ANDROID_LIBDL_STRTAB \
180    "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"
181#elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
182  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222
183  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789
184#  define ANDROID_LIBDL_STRTAB \
185    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0android_dlopen_ext\0"
186#else
187#  error Unsupported architecture. Only arm, arm64, mips, mips64, x86 and x86_64 are presently supported.
188#endif
189
190static ElfW(Sym) gLibDlSymtab[] = {
191  // Total length of libdl_info.strtab, including trailing 0.
192  // This is actually the STH_UNDEF entry. Technically, it's
193  // supposed to have st_name == 0, but instead, it points to an index
194  // in the strtab with a \0 to make iterating through the symtab easier.
195  ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
196  ELFW(SYM_INITIALIZER)(  0, &dlopen, 1),
197  ELFW(SYM_INITIALIZER)(  7, &dlclose, 1),
198  ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
199  ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
200  ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
201  ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
202  ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
203  ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
204  ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1),
205#if defined(__arm__)
206  ELFW(SYM_INITIALIZER)(130, &dl_unwind_find_exidx, 1),
207#endif
208};
209
210// Fake out a hash table with a single bucket.
211//
212// A search of the hash table will look through gLibDlSymtab starting with index 1, then
213// use gLibDlChains to find the next index to look at. gLibDlChains should be set up to
214// walk through every element in gLibDlSymtab, and then end with 0 (sentinel value).
215//
216// That is, gLibDlChains should look like { 0, 2, 3, ... N, 0 } where N is the number
217// of actual symbols, or nelems(gLibDlSymtab)-1 (since the first element of gLibDlSymtab is not
218// a real symbol). (See soinfo_elf_lookup().)
219//
220// Note that adding any new symbols here requires stubbing them out in libdl.
221static unsigned gLibDlBuckets[1] = { 1 };
222#if defined(__arm__)
223static unsigned gLibDlChains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0 };
224#else
225static unsigned gLibDlChains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
226#endif
227
228// This is used by the dynamic linker. Every process gets these symbols for free.
229soinfo libdl_info = {
230    "libdl.so",
231
232    .phdr = 0,
233    .phnum = 0,
234    .entry = 0,
235    .base = 0,
236    .size = 0,
237
238#if !defined(__LP64__)
239    .unused1 = 0,
240#endif
241
242    .dynamic = 0,
243
244#if !defined(__LP64__)
245    .unused2 = 0, .unused3 = 0,
246#endif
247
248    .next = 0,
249
250    .flags = FLAG_LINKED,
251
252    .strtab = ANDROID_LIBDL_STRTAB,
253    .symtab = gLibDlSymtab,
254
255    .nbucket = sizeof(gLibDlBuckets)/sizeof(unsigned),
256    .nchain = sizeof(gLibDlChains)/sizeof(unsigned),
257    .bucket = gLibDlBuckets,
258    .chain = gLibDlChains,
259
260#if defined(USE_RELA)
261    .plt_rela = 0,
262    .plt_rela_count = 0,
263    .rela = 0,
264    .rela_count = 0,
265#else
266    .plt_got = 0,
267    .plt_rel = 0,
268    .plt_rel_count = 0,
269    .rel = 0,
270    .rel_count = 0,
271#endif
272
273    .preinit_array = 0,
274    .preinit_array_count = 0,
275
276    .init_array = 0,
277    .init_array_count = 0,
278
279    .fini_array = 0,
280    .fini_array_count = 0,
281
282    .init_func = 0,
283    .fini_func = 0,
284
285#if defined(__arm__)
286    .ARM_exidx = 0,
287    .ARM_exidx_count = 0,
288#elif defined(__mips__)
289    .mips_symtabno = 0,
290    .mips_local_gotno = 0,
291    .mips_gotsym = 0,
292#endif
293
294    .ref_count = 0,
295    { .l_addr = 0, .l_name = 0, .l_ld = 0, .l_next = 0, .l_prev = 0, },
296    .constructors_called = false,
297    .load_bias = 0,
298#if !defined(__LP64__)
299    .has_text_relocations = false,
300#endif
301    .has_DT_SYMBOLIC = true,
302};
303