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/*
* 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 "linker.h"
/* This file hijacks the symbols stubbed out in libdl.so. */
#define DL_SUCCESS 0
#define DL_ERR_CANNOT_FIND_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 const char *dl_errors[] = {
[DL_SUCCESS] = NULL,
[DL_ERR_CANNOT_FIND_LIBRARY] = "Cannot find 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",
};
static int dl_last_err = DL_SUCCESS;
#define likely(expr) __builtin_expect (expr, 1)
#define unlikely(expr) __builtin_expect (expr, 0)
static pthread_mutex_t dl_lock = PTHREAD_MUTEX_INITIALIZER;
void *dlopen(const char *filename, int flag)
{
soinfo *ret;
pthread_mutex_lock(&dl_lock);
ret = find_library(filename);
if (unlikely(ret == NULL)) {
dl_last_err = DL_ERR_CANNOT_FIND_LIBRARY;
} else {
ret->refcount++;
}
pthread_mutex_unlock(&dl_lock);
return ret;
}
const char *dlerror(void)
{
const char *err = dl_errors[dl_last_err];
dl_last_err = DL_SUCCESS;
return err;
}
void *dlsym(void *handle, const char *symbol)
{
unsigned base;
Elf32_Sym *sym;
unsigned bind;
pthread_mutex_lock(&dl_lock);
if(unlikely(handle == 0)) {
dl_last_err = DL_ERR_INVALID_LIBRARY_HANDLE;
goto err;
}
if(unlikely(symbol == 0)) {
dl_last_err = DL_ERR_BAD_SYMBOL_NAME;
goto err;
}
if(handle == RTLD_DEFAULT) {
sym = lookup(symbol, &base);
} else if(handle == RTLD_NEXT) {
sym = lookup(symbol, &base);
} else {
sym = lookup_in_library((soinfo*) handle, symbol);
base = ((soinfo*) handle)->base;
}
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 + base;
pthread_mutex_unlock(&dl_lock);
return (void*)ret;
}
dl_last_err = DL_ERR_SYMBOL_NOT_GLOBAL;
}
else dl_last_err = DL_ERR_SYMBOL_NOT_FOUND;
err:
pthread_mutex_unlock(&dl_lock);
return 0;
}
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 233333333334444444444
// 0123456 78901234 567890 12345678 901234567890123456789
#define ANDROID_LIBDL_STRTAB \
"dlopen\0dlclose\0dlsym\0dlerror\0dl_unwind_find_exidx\0"
#elif defined(ANDROID_X86_LINKER)
// 0000000 00011111 111112 22222222 2333333333344444
// 0123456 78901234 567890 12345678 9012345678901234
#define ANDROID_LIBDL_STRTAB \
"dlopen\0dlclose\0dlsym\0dlerror\0dl_iterate_phdr\0"
#else /* !defined(ANDROID_ARM_LINKER) && !defined(ANDROID_X86_LINKER) */
#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,
},
#ifdef ANDROID_ARM_LINKER
{ st_name: 29,
st_value: (Elf32_Addr) &dl_unwind_find_exidx,
st_info: STB_GLOBAL << 4,
st_shndx: 1,
},
#elif defined(ANDROID_X86_LINKER)
{ st_name: 29,
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[6] = { 0, 2, 3, 4, 5, 0 };
soinfo libdl_info = {
name: "libdl.so",
flags: FLAG_LINKED,
strtab: ANDROID_LIBDL_STRTAB,
symtab: libdl_symtab,
nbucket: 1,
nchain: 6,
bucket: libdl_buckets,
chain: libdl_chains,
};
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