dlfcn.cpp revision 0266ae5f884d72da58f33a072e865ba131234a5e 
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  char** dlerror_slot = &reinterpret_cast<char**>(__get_tls())[TLS_SLOT_DLERROR];
35
36  const char* old_value = *dlerror_slot;
37  *dlerror_slot = new_value;
38  return old_value;
39}
40
41static void __bionic_format_dlerror(const char* msg, const char* detail) {
42  char* buffer = __get_thread()->dlerror_buffer;
43  strlcpy(buffer, msg, __BIONIC_DLERROR_BUFFER_SIZE);
44  if (detail != NULL) {
45    strlcat(buffer, ": ", __BIONIC_DLERROR_BUFFER_SIZE);
46    strlcat(buffer, detail, __BIONIC_DLERROR_BUFFER_SIZE);
47  }
48
49  __bionic_set_dlerror(buffer);
50}
51
52const char* dlerror() {
53  const char* old_value = __bionic_set_dlerror(NULL);
54  return old_value;
55}
56
57void android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) {
58  ScopedPthreadMutexLocker locker(&gDlMutex);
59  do_android_get_LD_LIBRARY_PATH(buffer, buffer_size);
60}
61
62void android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
63  ScopedPthreadMutexLocker locker(&gDlMutex);
64  do_android_update_LD_LIBRARY_PATH(ld_library_path);
65}
66
67void* dlopen(const char* filename, int flags) {
68  ScopedPthreadMutexLocker locker(&gDlMutex);
69  soinfo* result = do_dlopen(filename, flags);
70  if (result == NULL) {
71    __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
72    return NULL;
73  }
74  return result;
75}
76
77void* dlsym(void* handle, const char* symbol) {
78  ScopedPthreadMutexLocker locker(&gDlMutex);
79
80  if (handle == NULL) {
81    __bionic_format_dlerror("dlsym library handle is null", NULL);
82    return NULL;
83  }
84  if (symbol == NULL) {
85    __bionic_format_dlerror("dlsym symbol name is null", NULL);
86    return NULL;
87  }
88
89  soinfo* found = NULL;
90  ElfW(Sym)* sym = NULL;
91  if (handle == RTLD_DEFAULT) {
92    sym = dlsym_linear_lookup(symbol, &found, NULL);
93  } else if (handle == RTLD_NEXT) {
94    void* ret_addr = __builtin_return_address(0);
95    soinfo* si = find_containing_library(ret_addr);
96
97    sym = NULL;
98    if (si && si->next) {
99      sym = dlsym_linear_lookup(symbol, &found, si->next);
100    }
101  } else {
102    found = reinterpret_cast<soinfo*>(handle);
103    sym = dlsym_handle_lookup(found, symbol);
104  }
105
106  if (sym != NULL) {
107    unsigned bind = ELF_ST_BIND(sym->st_info);
108
109    if (bind == STB_GLOBAL && sym->st_shndx != 0) {
110      return reinterpret_cast<void*>(sym->st_value + found->load_bias);
111    }
112
113    __bionic_format_dlerror("symbol found but not global", symbol);
114    return NULL;
115  } else {
116    __bionic_format_dlerror("undefined symbol", symbol);
117    return NULL;
118  }
119}
120
121int dladdr(const void* addr, Dl_info* info) {
122  ScopedPthreadMutexLocker locker(&gDlMutex);
123
124  // Determine if this address can be found in any library currently mapped.
125  soinfo* si = find_containing_library(addr);
126  if (si == NULL) {
127    return 0;
128  }
129
130  memset(info, 0, sizeof(Dl_info));
131
132  info->dli_fname = si->name;
133  // Address at which the shared object is loaded.
134  info->dli_fbase = (void*) si->base;
135
136  // Determine if any symbol in the library contains the specified address.
137  ElfW(Sym)* sym = dladdr_find_symbol(si, addr);
138  if (sym != NULL) {
139    info->dli_sname = si->strtab + sym->st_name;
140    info->dli_saddr = (void*)(si->load_bias + sym->st_value);
141  }
142
143  return 1;
144}
145
146int dlclose(void* handle) {
147  ScopedPthreadMutexLocker locker(&gDlMutex);
148  return do_dlclose(reinterpret_cast<soinfo*>(handle));
149}
150
151// name_offset: starting index of the name in libdl_info.strtab
152#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
153    { name_offset, \
154      reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
155      /* st_size */ 0, \
156      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
157      /* st_other */ 0, \
158      shndx, \
159    }
160
161#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
162    { name_offset, \
163      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
164      /* st_other */ 0, \
165      shndx, \
166      reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
167      /* st_size */ 0, \
168    }
169
170#if defined(__arm__)
171  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1
172  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1
173#  define ANDROID_LIBDL_STRTAB \
174    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0dl_unwind_find_exidx\0"
175#elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
176  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1
177  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1
178#  define ANDROID_LIBDL_STRTAB \
179    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0"
180#else
181#  error Unsupported architecture. Only arm, arm64, mips, x86, and x86_64 are presently supported.
182#endif
183
184static ElfW(Sym) gLibDlSymtab[] = {
185  // Total length of libdl_info.strtab, including trailing 0.
186  // This is actually the STH_UNDEF entry. Technically, it's
187  // supposed to have st_name == 0, but instead, it points to an index
188  // in the strtab with a \0 to make iterating through the symtab easier.
189  ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
190  ELFW(SYM_INITIALIZER)(  0, &dlopen, 1),
191  ELFW(SYM_INITIALIZER)(  7, &dlclose, 1),
192  ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
193  ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
194  ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
195  ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
196  ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
197  ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
198#if defined(__arm__)
199  ELFW(SYM_INITIALIZER)(111, &dl_unwind_find_exidx, 1),
200#endif
201};
202
203// Fake out a hash table with a single bucket.
204//
205// A search of the hash table will look through gLibDlSymtab starting with index 1, then
206// use gLibDlChains to find the next index to look at. gLibDlChains should be set up to
207// walk through every element in gLibDlSymtab, and then end with 0 (sentinel value).
208//
209// That is, gLibDlChains should look like { 0, 2, 3, ... N, 0 } where N is the number
210// of actual symbols, or nelems(gLibDlSymtab)-1 (since the first element of gLibDlSymtab is not
211// a real symbol). (See soinfo_elf_lookup().)
212//
213// Note that adding any new symbols here requires stubbing them out in libdl.
214static unsigned gLibDlBuckets[1] = { 1 };
215#if defined(__arm__)
216static unsigned gLibDlChains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
217#else
218static unsigned gLibDlChains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 0 };
219#endif
220
221// This is used by the dynamic linker. Every process gets these symbols for free.
222soinfo libdl_info = {
223    "libdl.so",
224
225    .phdr = 0,
226    .phnum = 0,
227    .entry = 0,
228    .base = 0,
229    .size = 0,
230
231#if !defined(__LP64__)
232    .unused1 = 0,
233#endif
234
235    .dynamic = 0,
236
237#if !defined(__LP64__)
238    .unused2 = 0, .unused3 = 0,
239#endif
240
241    .next = 0,
242
243    .flags = FLAG_LINKED,
244
245    .strtab = ANDROID_LIBDL_STRTAB,
246    .symtab = gLibDlSymtab,
247
248    .nbucket = sizeof(gLibDlBuckets)/sizeof(unsigned),
249    .nchain = sizeof(gLibDlChains)/sizeof(unsigned),
250    .bucket = gLibDlBuckets,
251    .chain = gLibDlChains,
252
253#if defined(USE_RELA)
254    .plt_rela = 0,
255    .plt_rela_count = 0,
256    .rela = 0,
257    .rela_count = 0,
258#else
259    .plt_got = 0,
260    .plt_rel = 0,
261    .plt_rel_count = 0,
262    .rel = 0,
263    .rel_count = 0,
264#endif
265
266    .preinit_array = 0,
267    .preinit_array_count = 0,
268
269    .init_array = 0,
270    .init_array_count = 0,
271
272    .fini_array = 0,
273    .fini_array_count = 0,
274
275    .init_func = 0,
276    .fini_func = 0,
277
278#if defined(__arm__)
279    .ARM_exidx = 0,
280    .ARM_exidx_count = 0,
281#elif defined(__mips__)
282    .mips_symtabno = 0,
283    .mips_local_gotno = 0,
284    .mips_gotsym = 0,
285#endif
286
287    .ref_count = 0,
288    { .l_addr = 0, .l_name = 0, .l_ld = 0, .l_next = 0, .l_prev = 0, },
289    .constructors_called = false,
290    .load_bias = 0,
291#if !defined(__LP64__)
292    .has_text_relocations = false,
293#endif
294    .has_DT_SYMBOLIC = true,
295};
296