summaryrefslogtreecommitdiffstats
path: root/linker/dlfcn.c
blob: ac7e5d39c849515dc69c4b8708df2ff90abaefa3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include <dlfcn.h>
#include <pthread.h>
#include <stdio.h>
#include "linker.h"
#include "linker_format.h"

/* This file hijacks the symbols stubbed out in libdl.so. */

#define DL_SUCCESS                    0
#define DL_ERR_CANNOT_LOAD_LIBRARY    1
#define DL_ERR_INVALID_LIBRARY_HANDLE 2
#define DL_ERR_BAD_SYMBOL_NAME        3
#define DL_ERR_SYMBOL_NOT_FOUND       4
#define DL_ERR_SYMBOL_NOT_GLOBAL      5

static char dl_err_buf[1024];
static const char *dl_err_str;

static const char *dl_errors[] = {
    [DL_ERR_CANNOT_LOAD_LIBRARY] = "Cannot load library",
    [DL_ERR_INVALID_LIBRARY_HANDLE] = "Invalid library handle",
    [DL_ERR_BAD_SYMBOL_NAME] = "Invalid symbol name",
    [DL_ERR_SYMBOL_NOT_FOUND] = "Symbol not found",
    [DL_ERR_SYMBOL_NOT_GLOBAL] = "Symbol is not global",
};

#define likely(expr)   __builtin_expect (expr, 1)
#define unlikely(expr) __builtin_expect (expr, 0)

pthread_mutex_t dl_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;

static void set_dlerror(int err)
{
    format_buffer(dl_err_buf, sizeof(dl_err_buf), "%s: %s", dl_errors[err],
             linker_get_error());
    dl_err_str = (const char *)&dl_err_buf[0];
};

void *dlopen(const char *filename, int flag)
{
    soinfo *ret;

    pthread_mutex_lock(&dl_lock);
    ret = find_library(filename);
    if (unlikely(ret == NULL)) {
        set_dlerror(DL_ERR_CANNOT_LOAD_LIBRARY);
    } else {
        call_constructors_recursive(ret);
        ret->refcount++;
    }
    pthread_mutex_unlock(&dl_lock);
    return ret;
}

const char *dlerror(void)
{
    const char *tmp = dl_err_str;
    dl_err_str = NULL;
    return (const char *)tmp;
}

void *dlsym(void *handle, const char *symbol)
{
    soinfo *found;
    Elf32_Sym *sym;
    unsigned bind;

    pthread_mutex_lock(&dl_lock);

    if(unlikely(handle == 0)) { 
        set_dlerror(DL_ERR_INVALID_LIBRARY_HANDLE);
        goto err;
    }
    if(unlikely(symbol == 0)) {
        set_dlerror(DL_ERR_BAD_SYMBOL_NAME);
        goto err;
    }

    if(handle == RTLD_DEFAULT) {
        sym = lookup(symbol, &found, NULL);
    } else if(handle == RTLD_NEXT) {
        void *ret_addr = __builtin_return_address(0);
        soinfo *si = find_containing_library(ret_addr);

        sym = NULL;
        if(si && si->next) {
            sym = lookup(symbol, &found, si->next);
        }
    } else {
        found = (soinfo*)handle;
        sym = lookup_in_library(found, symbol);
    }

    if(likely(sym != 0)) {
        bind = ELF32_ST_BIND(sym->st_info);

        if(likely((bind == STB_GLOBAL) && (sym->st_shndx != 0))) {
            unsigned ret = sym->st_value + found->base;
            pthread_mutex_unlock(&dl_lock);
            return (void*)ret;
        }

        set_dlerror(DL_ERR_SYMBOL_NOT_GLOBAL);
    }
    else
        set_dlerror(DL_ERR_SYMBOL_NOT_FOUND);

err:
    pthread_mutex_unlock(&dl_lock);
    return 0;
}

int dladdr(const void *addr, Dl_info *info)
{
    int ret = 0;

    pthread_mutex_lock(&dl_lock);

    /* Determine if this address can be found in any library currently mapped */
    soinfo *si = find_containing_library(addr);

    if(si) {
        memset(info, 0, sizeof(Dl_info));

        info->dli_fname = si->name;
        info->dli_fbase = (void*)si->base;

        /* Determine if any symbol in the library contains the specified address */
        Elf32_Sym *sym = find_containing_symbol(addr, si);

        if(sym != NULL) {
            info->dli_sname = si->strtab + sym->st_name;
            info->dli_saddr = (void*)(si->base + sym->st_value);
        }

        ret = 1;
    }

    pthread_mutex_unlock(&dl_lock);

    return ret;
}

int dlclose(void *handle)
{
    pthread_mutex_lock(&dl_lock);
    (void)unload_library((soinfo*)handle);
    pthread_mutex_unlock(&dl_lock);
    return 0;
}

#if defined(ANDROID_ARM_LINKER)
//                     0000000 00011111 111112 22222222 2333333 333344444444445555555
//                     0123456 78901234 567890 12345678 9012345 678901234567890123456
#define ANDROID_LIBDL_STRTAB \
                      "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0dl_unwind_find_exidx\0"

#elif defined(ANDROID_X86_LINKER)
//                     0000000 00011111 111112 22222222 2333333 3333444444444455
//                     0123456 78901234 567890 12345678 9012345 6789012345678901
#define ANDROID_LIBDL_STRTAB \
                      "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0dl_iterate_phdr\0"
#else
#error Unsupported architecture. Only ARM and x86 are presently supported.
#endif


static Elf32_Sym libdl_symtab[] = {
      // total length of libdl_info.strtab, including trailing 0
      // This is actually the the STH_UNDEF entry. Technically, it's
      // supposed to have st_name == 0, but instead, it points to an index
      // in the strtab with a \0 to make iterating through the symtab easier.
    { st_name: sizeof(ANDROID_LIBDL_STRTAB) - 1,
    },
    { st_name: 0,   // starting index of the name in libdl_info.strtab
      st_value: (Elf32_Addr) &dlopen,
      st_info: STB_GLOBAL << 4,
      st_shndx: 1,
    },
    { st_name: 7,
      st_value: (Elf32_Addr) &dlclose,
      st_info: STB_GLOBAL << 4,
      st_shndx: 1,
    },
    { st_name: 15,
      st_value: (Elf32_Addr) &dlsym,
      st_info: STB_GLOBAL << 4,
      st_shndx: 1,
    },
    { st_name: 21,
      st_value: (Elf32_Addr) &dlerror,
      st_info: STB_GLOBAL << 4,
      st_shndx: 1,
    },
    { st_name: 29,
      st_value: (Elf32_Addr) &dladdr,
      st_info: STB_GLOBAL << 4,
      st_shndx: 1,
    },
#ifdef ANDROID_ARM_LINKER
    { st_name: 36,
      st_value: (Elf32_Addr) &dl_unwind_find_exidx,
      st_info: STB_GLOBAL << 4,
      st_shndx: 1,
    },
#elif defined(ANDROID_X86_LINKER)
    { st_name: 36,
      st_value: (Elf32_Addr) &dl_iterate_phdr,
      st_info: STB_GLOBAL << 4,
      st_shndx: 1,
    },
#endif
};

/* Fake out a hash table with a single bucket.
 * A search of the hash table will look through
 * libdl_symtab starting with index [1], then
 * use libdl_chains to find the next index to
 * look at.  libdl_chains should be set up to
 * walk through every element in libdl_symtab,
 * and then end with 0 (sentinel value).
 *
 * I.e., libdl_chains should look like
 * { 0, 2, 3, ... N, 0 } where N is the number
 * of actual symbols, or nelems(libdl_symtab)-1
 * (since the first element of libdl_symtab is not
 * a real symbol).
 *
 * (see _elf_lookup())
 *
 * Note that adding any new symbols here requires
 * stubbing them out in libdl.
 */
static unsigned libdl_buckets[1] = { 1 };
static unsigned libdl_chains[7] = { 0, 2, 3, 4, 5, 6, 0 };

soinfo libdl_info = {
    name: "libdl.so",
    flags: FLAG_LINKED,

    strtab: ANDROID_LIBDL_STRTAB,
    symtab: libdl_symtab,

    nbucket: 1,
    nchain: 7,
    bucket: libdl_buckets,
    chain: libdl_chains,
};