dlfcn.cpp revision e365f9d6543bc6607864ef61257505239dde15d1 
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_update_LD_LIBRARY_PATH(const char* ld_library_path) {
58  ScopedPthreadMutexLocker locker(&gDlMutex);
59  do_android_update_LD_LIBRARY_PATH(ld_library_path);
60}
61
62void* dlopen(const char* filename, int flags) {
63  ScopedPthreadMutexLocker locker(&gDlMutex);
64  soinfo* result = do_dlopen(filename, flags);
65  if (result == NULL) {
66    __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
67    return NULL;
68  }
69  return result;
70}
71
72void* dlsym(void* handle, const char* symbol) {
73  ScopedPthreadMutexLocker locker(&gDlMutex);
74
75  if (handle == NULL) {
76    __bionic_format_dlerror("dlsym library handle is null", NULL);
77    return NULL;
78  }
79  if (symbol == NULL) {
80    __bionic_format_dlerror("dlsym symbol name is null", NULL);
81    return NULL;
82  }
83
84  soinfo* found = NULL;
85  Elf_Sym* sym = NULL;
86  if (handle == RTLD_DEFAULT) {
87    sym = dlsym_linear_lookup(symbol, &found, NULL);
88  } else if (handle == RTLD_NEXT) {
89    void* ret_addr = __builtin_return_address(0);
90    soinfo* si = find_containing_library(ret_addr);
91
92    sym = NULL;
93    if (si && si->next) {
94      sym = dlsym_linear_lookup(symbol, &found, si->next);
95    }
96  } else {
97    found = reinterpret_cast<soinfo*>(handle);
98    sym = dlsym_handle_lookup(found, symbol);
99  }
100
101  if (sym != NULL) {
102    unsigned bind = ELF_ST_BIND(sym->st_info);
103
104    if (bind == STB_GLOBAL && sym->st_shndx != 0) {
105      return reinterpret_cast<void*>(sym->st_value + found->load_bias);
106    }
107
108    __bionic_format_dlerror("symbol found but not global", symbol);
109    return NULL;
110  } else {
111    __bionic_format_dlerror("undefined symbol", symbol);
112    return NULL;
113  }
114}
115
116int dladdr(const void* addr, Dl_info* info) {
117  ScopedPthreadMutexLocker locker(&gDlMutex);
118
119  // Determine if this address can be found in any library currently mapped.
120  soinfo* si = find_containing_library(addr);
121  if (si == NULL) {
122    return 0;
123  }
124
125  memset(info, 0, sizeof(Dl_info));
126
127  info->dli_fname = si->name;
128  // Address at which the shared object is loaded.
129  info->dli_fbase = (void*) si->base;
130
131  // Determine if any symbol in the library contains the specified address.
132  Elf_Sym *sym = dladdr_find_symbol(si, addr);
133  if (sym != NULL) {
134    info->dli_sname = si->strtab + sym->st_name;
135    info->dli_saddr = (void*)(si->load_bias + sym->st_value);
136  }
137
138  return 1;
139}
140
141int dlclose(void* handle) {
142  ScopedPthreadMutexLocker locker(&gDlMutex);
143  return do_dlclose(reinterpret_cast<soinfo*>(handle));
144}
145
146#if defined(__arm__)
147//   0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888 8888888
148//   0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012 3456789
149#define ANDROID_LIBDL_STRTAB \
150    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0dl_iterate_phdr\0dl_unwind_find_exidx\0"
151#elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
152//   0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667
153//   0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890
154#define ANDROID_LIBDL_STRTAB \
155    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0dl_iterate_phdr\0"
156#else
157#error Unsupported architecture. Only aarch64, arm, mips, x86, and x86_64 are presently supported.
158#endif
159
160// name_offset: starting index of the name in libdl_info.strtab
161#define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
162    { name_offset, \
163      reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
164      /* st_size */ 0, \
165      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
166      /* st_other */ 0, \
167      shndx, \
168    }
169
170#define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
171    { name_offset, \
172      (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
173      /* st_other */ 0, \
174      shndx, \
175      reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
176      /* st_size */ 0, \
177    }
178
179#if defined(__LP64__)
180#  define ELF_SYM_INITIALIZER ELF64_SYM_INITIALIZER
181#else
182#  define ELF_SYM_INITIALIZER ELF32_SYM_INITIALIZER
183#endif
184
185static Elf_Sym gLibDlSymtab[] = {
186  // Total length of libdl_info.strtab, including trailing 0.
187  // This is actually the STH_UNDEF entry. Technically, it's
188  // supposed to have st_name == 0, but instead, it points to an index
189  // in the strtab with a \0 to make iterating through the symtab easier.
190  ELF_SYM_INITIALIZER(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
191  ELF_SYM_INITIALIZER( 0, &dlopen, 1),
192  ELF_SYM_INITIALIZER( 7, &dlclose, 1),
193  ELF_SYM_INITIALIZER(15, &dlsym, 1),
194  ELF_SYM_INITIALIZER(21, &dlerror, 1),
195  ELF_SYM_INITIALIZER(29, &dladdr, 1),
196  ELF_SYM_INITIALIZER(36, &android_update_LD_LIBRARY_PATH, 1),
197  ELF_SYM_INITIALIZER(67, &dl_iterate_phdr, 1),
198#if defined(__arm__)
199  ELF_SYM_INITIALIZER(83, &dl_unwind_find_exidx, 1),
200#endif
201};
202
203// Fake out a hash table with a single bucket.
204// A search of the hash table will look through
205// gLibDlSymtab starting with index [1], then
206// use gLibDlChains to find the next index to
207// look at.  gLibDlChains should be set up to
208// walk through every element in gLibDlSymtab,
209// and then end with 0 (sentinel value).
210//
211// That is, gLibDlChains should look like
212// { 0, 2, 3, ... N, 0 } where N is the number
213// of actual symbols, or nelems(gLibDlSymtab)-1
214// (since the first element of gLibDlSymtab is not
215// a real symbol).
216//
217// (see soinfo_elf_lookup())
218//
219// Note that adding any new symbols here requires
220// stubbing them out in libdl.
221static unsigned gLibDlBuckets[1] = { 1 };
222#if defined(__arm__)
223static unsigned gLibDlChains[9] = { 0, 2, 3, 4, 5, 6, 7, 8, 0 };
224#else
225static unsigned gLibDlChains[8] = { 0, 2, 3, 4, 5, 6, 7, 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