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bionic/linker/linker.cpp
Christopher Ferris 6bec5b792a Small cleanup of soinfo_elf_lookup. 
- Remove unnecessary line.
- Move declarations to first use.

Change-Id: I1d8398d6c13f7cb86bffe0b68af849e35a4b234d
2013-06-03 20:15:14 -07:00

1837 lines
59 KiB
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/*
* Copyright (C) 2008, 2009 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/auxvec.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/atomics.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
// Private C library headers.
#include <private/bionic_tls.h>
#include <private/KernelArgumentBlock.h>
#include <private/ScopedPthreadMutexLocker.h>
#include "linker.h"
#include "linker_debug.h"
#include "linker_environ.h"
#include "linker_phdr.h"
/* Assume average path length of 64 and max 8 paths */
#define LDPATH_BUFSIZE 512
#define LDPATH_MAX 8
#define LDPRELOAD_BUFSIZE 512
#define LDPRELOAD_MAX 8
/* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<<
*
* Do NOT use malloc() and friends or pthread_*() code here.
* Don't use printf() either; it's caused mysterious memory
* corruption in the past.
* The linker runs before we bring up libc and it's easiest
* to make sure it does not depend on any complex libc features
*
* open issues / todo:
*
* - are we doing everything we should for ARM_COPY relocations?
* - cleaner error reporting
* - after linking, set as much stuff as possible to READONLY
* and NOEXEC
*/
static bool soinfo_link_image(soinfo* si);
// We can't use malloc(3) in the dynamic linker. We use a linked list of anonymous
// maps, each a single page in size. The pages are broken up into as many struct soinfo
// objects as will fit, and they're all threaded together on a free list.
#define SOINFO_PER_POOL ((PAGE_SIZE - sizeof(soinfo_pool_t*)) / sizeof(soinfo))
struct soinfo_pool_t {
soinfo_pool_t* next;
soinfo info[SOINFO_PER_POOL];
};
static struct soinfo_pool_t* gSoInfoPools = NULL;
static soinfo* gSoInfoFreeList = NULL;
static soinfo* solist = &libdl_info;
static soinfo* sonext = &libdl_info;
static soinfo* somain; /* main process, always the one after libdl_info */
static const char* const gSoPaths[] = {
"/vendor/lib",
"/system/lib",
NULL
};
static char gLdPathsBuffer[LDPATH_BUFSIZE];
static const char* gLdPaths[LDPATH_MAX + 1];
static char gLdPreloadsBuffer[LDPRELOAD_BUFSIZE];
static const char* gLdPreloadNames[LDPRELOAD_MAX + 1];
static soinfo* gLdPreloads[LDPRELOAD_MAX + 1];
__LIBC_HIDDEN__ int gLdDebugVerbosity;
__LIBC_HIDDEN__ abort_msg_t* gAbortMessage = NULL; // For debuggerd.
enum RelocationKind {
kRelocAbsolute = 0,
kRelocRelative,
kRelocCopy,
kRelocSymbol,
kRelocMax
};
#if STATS
struct linker_stats_t {
int count[kRelocMax];
};
static linker_stats_t linker_stats;
static void count_relocation(RelocationKind kind) {
++linker_stats.count[kind];
}
#else
static void count_relocation(RelocationKind) {
}
#endif
#if COUNT_PAGES
static unsigned bitmask[4096];
#define MARK(offset) \
do { \
bitmask[((offset) >> 12) >> 3] |= (1 << (((offset) >> 12) & 7)); \
} while(0)
#else
#define MARK(x) do {} while (0)
#endif
// You shouldn't try to call memory-allocating functions in the dynamic linker.
// Guard against the most obvious ones.
#define DISALLOW_ALLOCATION(return_type, name, ...) \
return_type name __VA_ARGS__ \
{ \
const char* msg = "ERROR: " #name " called from the dynamic linker!\n"; \
__libc_format_log(ANDROID_LOG_FATAL, "linker", "%s", msg); \
write(2, msg, strlen(msg)); \
abort(); \
}
#define UNUSED __attribute__((unused))
DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED));
DISALLOW_ALLOCATION(void, free, (void* u UNUSED));
DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED));
DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED));
static char tmp_err_buf[768];
static char __linker_dl_err_buf[768];
char* linker_get_error_buffer() {
return &__linker_dl_err_buf[0];
}
size_t linker_get_error_buffer_size() {
return sizeof(__linker_dl_err_buf);
}
/*
* This function is an empty stub where GDB locates a breakpoint to get notified
* about linker activity.
*/
extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity();
static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, RT_CONSISTENT, 0};
static link_map_t* r_debug_tail = 0;
static pthread_mutex_t gDebugMutex = PTHREAD_MUTEX_INITIALIZER;
static void insert_soinfo_into_debug_map(soinfo * info) {
// Copy the necessary fields into the debug structure.
link_map_t* map = &(info->link_map);
map->l_addr = info->base;
map->l_name = (char*) info->name;
map->l_ld = (uintptr_t)info->dynamic;
/* Stick the new library at the end of the list.
* gdb tends to care more about libc than it does
* about leaf libraries, and ordering it this way
* reduces the back-and-forth over the wire.
*/
if (r_debug_tail) {
r_debug_tail->l_next = map;
map->l_prev = r_debug_tail;
map->l_next = 0;
} else {
_r_debug.r_map = map;
map->l_prev = 0;
map->l_next = 0;
}
r_debug_tail = map;
}
static void remove_soinfo_from_debug_map(soinfo* info) {
link_map_t* map = &(info->link_map);
if (r_debug_tail == map) {
r_debug_tail = map->l_prev;
}
if (map->l_prev) {
map->l_prev->l_next = map->l_next;
}
if (map->l_next) {
map->l_next->l_prev = map->l_prev;
}
}
static void notify_gdb_of_load(soinfo* info) {
if (info->flags & FLAG_EXE) {
// GDB already knows about the main executable
return;
}
ScopedPthreadMutexLocker locker(&gDebugMutex);
_r_debug.r_state = RT_ADD;
rtld_db_dlactivity();
insert_soinfo_into_debug_map(info);
_r_debug.r_state = RT_CONSISTENT;
rtld_db_dlactivity();
}
static void notify_gdb_of_unload(soinfo* info) {
if (info->flags & FLAG_EXE) {
// GDB already knows about the main executable
return;
}
ScopedPthreadMutexLocker locker(&gDebugMutex);
_r_debug.r_state = RT_DELETE;
rtld_db_dlactivity();
remove_soinfo_from_debug_map(info);
_r_debug.r_state = RT_CONSISTENT;
rtld_db_dlactivity();
}
void notify_gdb_of_libraries() {
_r_debug.r_state = RT_ADD;
rtld_db_dlactivity();
_r_debug.r_state = RT_CONSISTENT;
rtld_db_dlactivity();
}
static bool ensure_free_list_non_empty() {
if (gSoInfoFreeList != NULL) {
return true;
}
// Allocate a new pool.
soinfo_pool_t* pool = reinterpret_cast<soinfo_pool_t*>(mmap(NULL, sizeof(*pool),
PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, 0, 0));
if (pool == MAP_FAILED) {
return false;
}
// Add the pool to our list of pools.
pool->next = gSoInfoPools;
gSoInfoPools = pool;
// Chain the entries in the new pool onto the free list.
gSoInfoFreeList = &pool->info[0];
soinfo* next = NULL;
for (int i = SOINFO_PER_POOL - 1; i >= 0; --i) {
pool->info[i].next = next;
next = &pool->info[i];
}
return true;
}
static void set_soinfo_pool_protection(int protection) {
for (soinfo_pool_t* p = gSoInfoPools; p != NULL; p = p->next) {
if (mprotect(p, sizeof(*p), protection) == -1) {
abort(); // Can't happen.
}
}
}
static soinfo* soinfo_alloc(const char* name) {
if (strlen(name) >= SOINFO_NAME_LEN) {
DL_ERR("library name \"%s\" too long", name);
return NULL;
}
if (!ensure_free_list_non_empty()) {
DL_ERR("out of memory when loading \"%s\"", name);
return NULL;
}
// Take the head element off the free list.
soinfo* si = gSoInfoFreeList;
gSoInfoFreeList = gSoInfoFreeList->next;
// Initialize the new element.
memset(si, 0, sizeof(soinfo));
strlcpy(si->name, name, sizeof(si->name));
sonext->next = si;
sonext = si;
TRACE("name %s: allocated soinfo @ %p", name, si);
return si;
}
static void soinfo_free(soinfo* si)
{
if (si == NULL) {
return;
}
soinfo *prev = NULL, *trav;
TRACE("name %s: freeing soinfo @ %p", si->name, si);
for (trav = solist; trav != NULL; trav = trav->next) {
if (trav == si)
break;
prev = trav;
}
if (trav == NULL) {
/* si was not in solist */
DL_ERR("name \"%s\" is not in solist!", si->name);
return;
}
/* prev will never be NULL, because the first entry in solist is
always the static libdl_info.
*/
prev->next = si->next;
if (si == sonext) {
sonext = prev;
}
si->next = gSoInfoFreeList;
gSoInfoFreeList = si;
}
static void parse_path(const char* path, const char* delimiters,
const char** array, char* buf, size_t buf_size, size_t max_count) {
if (path == NULL) {
return;
}
size_t len = strlcpy(buf, path, buf_size);
size_t i = 0;
char* buf_p = buf;
while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) {
if (*array[i] != '\0') {
++i;
}
}
// Forget the last path if we had to truncate; this occurs if the 2nd to
// last char isn't '\0' (i.e. wasn't originally a delimiter).
if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') {
array[i - 1] = NULL;
} else {
array[i] = NULL;
}
}
static void parse_LD_LIBRARY_PATH(const char* path) {
parse_path(path, ":", gLdPaths,
gLdPathsBuffer, sizeof(gLdPathsBuffer), LDPATH_MAX);
}
static void parse_LD_PRELOAD(const char* path) {
// We have historically supported ':' as well as ' ' in LD_PRELOAD.
parse_path(path, " :", gLdPreloadNames,
gLdPreloadsBuffer, sizeof(gLdPreloadsBuffer), LDPRELOAD_MAX);
}
#ifdef ANDROID_ARM_LINKER
/* For a given PC, find the .so that it belongs to.
* Returns the base address of the .ARM.exidx section
* for that .so, and the number of 8-byte entries
* in that section (via *pcount).
*
* Intended to be called by libc's __gnu_Unwind_Find_exidx().
*
* This function is exposed via dlfcn.cpp and libdl.so.
*/
_Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount)
{
soinfo *si;
unsigned addr = (unsigned)pc;
for (si = solist; si != 0; si = si->next){
if ((addr >= si->base) && (addr < (si->base + si->size))) {
*pcount = si->ARM_exidx_count;
return (_Unwind_Ptr)si->ARM_exidx;
}
}
*pcount = 0;
return NULL;
}
#elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER)
/* Here, we only have to provide a callback to iterate across all the
* loaded libraries. gcc_eh does the rest. */
int
dl_iterate_phdr(int (*cb)(dl_phdr_info *info, size_t size, void *data),
void *data)
{
int rv = 0;
for (soinfo* si = solist; si != NULL; si = si->next) {
dl_phdr_info dl_info;
dl_info.dlpi_addr = si->link_map.l_addr;
dl_info.dlpi_name = si->link_map.l_name;
dl_info.dlpi_phdr = si->phdr;
dl_info.dlpi_phnum = si->phnum;
rv = cb(&dl_info, sizeof(dl_phdr_info), data);
if (rv != 0) {
break;
}
}
return rv;
}
#endif
static Elf32_Sym* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) {
Elf32_Sym* symtab = si->symtab;
const char* strtab = si->strtab;
TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d",
name, si->name, si->base, hash, hash % si->nbucket);
for (unsigned n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]) {
Elf32_Sym* s = symtab + n;
if (strcmp(strtab + s->st_name, name)) continue;
/* only concern ourselves with global and weak symbol definitions */
switch(ELF32_ST_BIND(s->st_info)){
case STB_GLOBAL:
case STB_WEAK:
if (s->st_shndx == SHN_UNDEF) {
continue;
}
TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d",
name, si->name, s->st_value, s->st_size);
return s;
}
}
return NULL;
}
static unsigned elfhash(const char* _name) {
const unsigned char* name = (const unsigned char*) _name;
unsigned h = 0, g;
while(*name) {
h = (h << 4) + *name++;
g = h & 0xf0000000;
h ^= g;
h ^= g >> 24;
}
return h;
}
static Elf32_Sym* soinfo_do_lookup(soinfo* si, const char* name, soinfo** lsi, soinfo* needed[]) {
unsigned elf_hash = elfhash(name);
Elf32_Sym* s = NULL;
if (si != NULL && somain != NULL) {
/*
* Local scope is executable scope. Just start looking into it right away
* for the shortcut.
*/
if (si == somain) {
s = soinfo_elf_lookup(si, elf_hash, name);
if (s != NULL) {
*lsi = si;
goto done;
}
} else {
/* Order of symbol lookup is controlled by DT_SYMBOLIC flag */
/*
* If this object was built with symbolic relocations disabled, the
* first place to look to resolve external references is the main
* executable.
*/
if (!si->has_DT_SYMBOLIC) {
DEBUG("%s: looking up %s in executable %s",
si->name, name, somain->name);
s = soinfo_elf_lookup(somain, elf_hash, name);
if (s != NULL) {
*lsi = somain;
goto done;
}
}
/* Look for symbols in the local scope (the object who is
* searching). This happens with C++ templates on i386 for some
* reason.
*
* Notes on weak symbols:
* The ELF specs are ambiguous about treatment of weak definitions in
* dynamic linking. Some systems return the first definition found
* and some the first non-weak definition. This is system dependent.
* Here we return the first definition found for simplicity. */
s = soinfo_elf_lookup(si, elf_hash, name);
if (s != NULL) {
*lsi = si;
goto done;
}
/*
* If this object was built with -Bsymbolic and symbol is not found
* in the local scope, try to find the symbol in the main executable.
*/
if (si->has_DT_SYMBOLIC) {
DEBUG("%s: looking up %s in executable %s after local scope",
si->name, name, somain->name);
s = soinfo_elf_lookup(somain, elf_hash, name);
if (s != NULL) {
*lsi = somain;
goto done;
}
}
}
}
/* Next, look for it in the preloads list */
for (int i = 0; gLdPreloads[i] != NULL; i++) {
s = soinfo_elf_lookup(gLdPreloads[i], elf_hash, name);
if (s != NULL) {
*lsi = gLdPreloads[i];
goto done;
}
}
for (int i = 0; needed[i] != NULL; i++) {
DEBUG("%s: looking up %s in %s",
si->name, name, needed[i]->name);
s = soinfo_elf_lookup(needed[i], elf_hash, name);
if (s != NULL) {
*lsi = needed[i];
goto done;
}
}
done:
if (s != NULL) {
TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, "
"found in %s, base = 0x%08x, load bias = 0x%08x",
si->name, name, s->st_value,
(*lsi)->name, (*lsi)->base, (*lsi)->load_bias);
return s;
}
return NULL;
}
/* This is used by dlsym(3). It performs symbol lookup only within the
specified soinfo object and not in any of its dependencies.
TODO: Only looking in the specified soinfo seems wrong. dlsym(3) says
that it should do a breadth first search through the dependency
tree. This agrees with the ELF spec (aka System V Application
Binary Interface) where in Chapter 5 it discuss resolving "Shared
Object Dependencies" in breadth first search order.
*/
Elf32_Sym* dlsym_handle_lookup(soinfo* si, const char* name)
{
return soinfo_elf_lookup(si, elfhash(name), name);
}
/* This is used by dlsym(3) to performs a global symbol lookup. If the
start value is null (for RTLD_DEFAULT), the search starts at the
beginning of the global solist. Otherwise the search starts at the
specified soinfo (for RTLD_NEXT).
*/
Elf32_Sym* dlsym_linear_lookup(const char* name, soinfo** found, soinfo* start) {
unsigned elf_hash = elfhash(name);
if (start == NULL) {
start = solist;
}
Elf32_Sym* s = NULL;
for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) {
s = soinfo_elf_lookup(si, elf_hash, name);
if (s != NULL) {
*found = si;
break;
}
}
if (s != NULL) {
TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, found->base = 0x%08x",
name, s->st_value, (*found)->base);
}
return s;
}
soinfo* find_containing_library(const void* p) {
Elf32_Addr address = reinterpret_cast<Elf32_Addr>(p);
for (soinfo* si = solist; si != NULL; si = si->next) {
if (address >= si->base && address - si->base < si->size) {
return si;
}
}
return NULL;
}
Elf32_Sym* dladdr_find_symbol(soinfo* si, const void* addr) {
Elf32_Addr soaddr = reinterpret_cast<Elf32_Addr>(addr) - si->base;
// Search the library's symbol table for any defined symbol which
// contains this address.
for (size_t i = 0; i < si->nchain; ++i) {
Elf32_Sym* sym = &si->symtab[i];
if (sym->st_shndx != SHN_UNDEF &&
soaddr >= sym->st_value &&
soaddr < sym->st_value + sym->st_size) {
return sym;
}
}
return NULL;
}
#if 0
static void dump(soinfo* si)
{
Elf32_Sym* s = si->symtab;
for (unsigned n = 0; n < si->nchain; n++) {
TRACE("%04d> %08x: %02x %04x %08x %08x %s", n, s,
s->st_info, s->st_shndx, s->st_value, s->st_size,
si->strtab + s->st_name);
s++;
}
}
#endif
static int open_library_on_path(const char* name, const char* const paths[]) {
char buf[512];
for (size_t i = 0; paths[i] != NULL; ++i) {
int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name);
if (n < 0 || n >= static_cast<int>(sizeof(buf))) {
PRINT("Warning: ignoring very long library path: %s/%s", paths[i], name);
continue;
}
int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC));
if (fd != -1) {
return fd;
}
}
return -1;
}
static int open_library(const char* name) {
TRACE("[ opening %s ]", name);
// If the name contains a slash, we should attempt to open it directly and not search the paths.
if (strchr(name, '/') != NULL) {
int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC));
if (fd != -1) {
return fd;
}
// ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now.
}
// Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths.
int fd = open_library_on_path(name, gLdPaths);
if (fd == -1) {
fd = open_library_on_path(name, gSoPaths);
}
return fd;
}
static soinfo* load_library(const char* name) {
// Open the file.
int fd = open_library(name);
if (fd == -1) {
DL_ERR("library \"%s\" not found", name);
return NULL;
}
// Read the ELF header and load the segments.
ElfReader elf_reader(name, fd);
if (!elf_reader.Load()) {
return NULL;
}
const char* bname = strrchr(name, '/');
soinfo* si = soinfo_alloc(bname ? bname + 1 : name);
if (si == NULL) {
return NULL;
}
si->base = elf_reader.load_start();
si->size = elf_reader.load_size();
si->load_bias = elf_reader.load_bias();
si->flags = 0;
si->entry = 0;
si->dynamic = NULL;
si->phnum = elf_reader.phdr_count();
si->phdr = elf_reader.loaded_phdr();
return si;
}
static soinfo *find_loaded_library(const char *name)
{
soinfo *si;
const char *bname;
// TODO: don't use basename only for determining libraries
// http://code.google.com/p/android/issues/detail?id=6670
bname = strrchr(name, '/');
bname = bname ? bname + 1 : name;
for (si = solist; si != NULL; si = si->next) {
if (!strcmp(bname, si->name)) {
return si;
}
}
return NULL;
}
static soinfo* find_library_internal(const char* name) {
if (name == NULL) {
return somain;
}
soinfo* si = find_loaded_library(name);
if (si != NULL) {
if (si->flags & FLAG_LINKED) {
return si;
}
DL_ERR("OOPS: recursive link to \"%s\"", si->name);
return NULL;
}
TRACE("[ '%s' has not been loaded yet. Locating...]", name);
si = load_library(name);
if (si == NULL) {
return NULL;
}
// At this point we know that whatever is loaded @ base is a valid ELF
// shared library whose segments are properly mapped in.
TRACE("[ init_library base=0x%08x sz=0x%08x name='%s' ]",
si->base, si->size, si->name);
if (!soinfo_link_image(si)) {
munmap(reinterpret_cast<void*>(si->base), si->size);
soinfo_free(si);
return NULL;
}
return si;
}
static soinfo* find_library(const char* name) {
soinfo* si = find_library_internal(name);
if (si != NULL) {
si->ref_count++;
}
return si;
}
static int soinfo_unload(soinfo* si) {
if (si->ref_count == 1) {
TRACE("unloading '%s'", si->name);
si->CallDestructors();
for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) {
if (d->d_tag == DT_NEEDED) {
const char* library_name = si->strtab + d->d_un.d_val;
TRACE("%s needs to unload %s", si->name, library_name);
soinfo_unload(find_loaded_library(library_name));
}
}
munmap(reinterpret_cast<void*>(si->base), si->size);
notify_gdb_of_unload(si);
soinfo_free(si);
si->ref_count = 0;
} else {
si->ref_count--;
TRACE("not unloading '%s', decrementing ref_count to %d", si->name, si->ref_count);
}
return 0;
}
void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
if (!get_AT_SECURE()) {
parse_LD_LIBRARY_PATH(ld_library_path);
}
}
soinfo* do_dlopen(const char* name, int flags) {
if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL)) != 0) {
DL_ERR("invalid flags to dlopen: %x", flags);
return NULL;
}
set_soinfo_pool_protection(PROT_READ | PROT_WRITE);
soinfo* si = find_library(name);
if (si != NULL) {
si->CallConstructors();
}
set_soinfo_pool_protection(PROT_READ);
return si;
}
int do_dlclose(soinfo* si) {
set_soinfo_pool_protection(PROT_READ | PROT_WRITE);
int result = soinfo_unload(si);
set_soinfo_pool_protection(PROT_READ);
return result;
}
/* TODO: don't use unsigned for addrs below. It works, but is not
* ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned
* long.
*/
static int soinfo_relocate(soinfo* si, Elf32_Rel* rel, unsigned count,
soinfo* needed[])
{
Elf32_Sym* symtab = si->symtab;
const char* strtab = si->strtab;
Elf32_Sym* s;
Elf32_Rel* start = rel;
soinfo* lsi;
for (size_t idx = 0; idx < count; ++idx, ++rel) {
unsigned type = ELF32_R_TYPE(rel->r_info);
unsigned sym = ELF32_R_SYM(rel->r_info);
Elf32_Addr reloc = static_cast<Elf32_Addr>(rel->r_offset + si->load_bias);
Elf32_Addr sym_addr = 0;
char* sym_name = NULL;
DEBUG("Processing '%s' relocation at index %d", si->name, idx);
if (type == 0) { // R_*_NONE
continue;
}
if (sym != 0) {
sym_name = (char *)(strtab + symtab[sym].st_name);
s = soinfo_do_lookup(si, sym_name, &lsi, needed);
if (s == NULL) {
/* We only allow an undefined symbol if this is a weak
reference.. */
s = &symtab[sym];
if (ELF32_ST_BIND(s->st_info) != STB_WEAK) {
DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name);
return -1;
}
/* IHI0044C AAELF 4.5.1.1:
Libraries are not searched to resolve weak references.
It is not an error for a weak reference to remain
unsatisfied.
During linking, the value of an undefined weak reference is:
- Zero if the relocation type is absolute
- The address of the place if the relocation is pc-relative
- The address of nominal base address if the relocation
type is base-relative.
*/
switch (type) {
#if defined(ANDROID_ARM_LINKER)
case R_ARM_JUMP_SLOT:
case R_ARM_GLOB_DAT:
case R_ARM_ABS32:
case R_ARM_RELATIVE: /* Don't care. */
#elif defined(ANDROID_X86_LINKER)
case R_386_JMP_SLOT:
case R_386_GLOB_DAT:
case R_386_32:
case R_386_RELATIVE: /* Dont' care. */
#endif /* ANDROID_*_LINKER */
/* sym_addr was initialized to be zero above or relocation
code below does not care about value of sym_addr.
No need to do anything. */
break;
#if defined(ANDROID_X86_LINKER)
case R_386_PC32:
sym_addr = reloc;
break;
#endif /* ANDROID_X86_LINKER */
#if defined(ANDROID_ARM_LINKER)
case R_ARM_COPY:
/* Fall through. Can't really copy if weak symbol is
not found in run-time. */
#endif /* ANDROID_ARM_LINKER */
default:
DL_ERR("unknown weak reloc type %d @ %p (%d)",
type, rel, (int) (rel - start));
return -1;
}
} else {
/* We got a definition. */
#if 0
if ((base == 0) && (si->base != 0)) {
/* linking from libraries to main image is bad */
DL_ERR("cannot locate \"%s\"...",
strtab + symtab[sym].st_name);
return -1;
}
#endif
sym_addr = static_cast<Elf32_Addr>(s->st_value + lsi->load_bias);
}
count_relocation(kRelocSymbol);
} else {
s = NULL;
}
/* TODO: This is ugly. Split up the relocations by arch into
* different files.
*/
switch(type){
#if defined(ANDROID_ARM_LINKER)
case R_ARM_JUMP_SLOT:
count_relocation(kRelocAbsolute);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name);
*reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr;
break;
case R_ARM_GLOB_DAT:
count_relocation(kRelocAbsolute);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name);
*reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr;
break;
case R_ARM_ABS32:
count_relocation(kRelocAbsolute);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s", reloc, sym_addr, sym_name);
*reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr;
break;
case R_ARM_REL32:
count_relocation(kRelocRelative);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s",
reloc, sym_addr, rel->r_offset, sym_name);
*reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr - rel->r_offset;
break;
#elif defined(ANDROID_X86_LINKER)
case R_386_JMP_SLOT:
count_relocation(kRelocAbsolute);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name);
*reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr;
break;
case R_386_GLOB_DAT:
count_relocation(kRelocAbsolute);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name);
*reinterpret_cast<Elf32_Addr*>(reloc) = sym_addr;
break;
#elif defined(ANDROID_MIPS_LINKER)
case R_MIPS_REL32:
count_relocation(kRelocAbsolute);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s",
reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*");
if (s) {
*reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr;
} else {
*reinterpret_cast<Elf32_Addr*>(reloc) += si->base;
}
break;
#endif /* ANDROID_*_LINKER */
#if defined(ANDROID_ARM_LINKER)
case R_ARM_RELATIVE:
#elif defined(ANDROID_X86_LINKER)
case R_386_RELATIVE:
#endif /* ANDROID_*_LINKER */
count_relocation(kRelocRelative);
MARK(rel->r_offset);
if (sym) {
DL_ERR("odd RELATIVE form...");
return -1;
}
TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x", reloc, si->base);
*reinterpret_cast<Elf32_Addr*>(reloc) += si->base;
break;
#if defined(ANDROID_X86_LINKER)
case R_386_32:
count_relocation(kRelocRelative);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s", reloc, sym_addr, sym_name);
*reinterpret_cast<Elf32_Addr*>(reloc) += sym_addr;
break;
case R_386_PC32:
count_relocation(kRelocRelative);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s",
reloc, (sym_addr - reloc), sym_addr, reloc, sym_name);
*reinterpret_cast<Elf32_Addr*>(reloc) += (sym_addr - reloc);
break;
#endif /* ANDROID_X86_LINKER */
#ifdef ANDROID_ARM_LINKER
case R_ARM_COPY:
if ((si->flags & FLAG_EXE) == 0) {
/*
* http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf
*
* Section 4.7.1.10 "Dynamic relocations"
* R_ARM_COPY may only appear in executable objects where e_type is
* set to ET_EXEC.
*
* TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables.
* We should explicitly disallow ET_DYN executables from having
* R_ARM_COPY relocations.
*/
DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name);
return -1;
}
count_relocation(kRelocCopy);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s", reloc, s->st_size, sym_addr, sym_name);
if (reloc == sym_addr) {
Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed);
if (src == NULL) {
DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name);
return -1;
}
if (lsi->has_DT_SYMBOLIC) {
DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared "
"library %s (built with -Bsymbolic?)", si->name, lsi->name);
return -1;
}
if (s->st_size < src->st_size) {
DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)",
si->name, s->st_size, src->st_size);
return -1;
}
memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size);
} else {
DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name);
return -1;
}
break;
#endif /* ANDROID_ARM_LINKER */
default:
DL_ERR("unknown reloc type %d @ %p (%d)",
type, rel, (int) (rel - start));
return -1;
}
}
return 0;
}
#ifdef ANDROID_MIPS_LINKER
static int mips_relocate_got(soinfo* si, soinfo* needed[]) {
unsigned *got;
unsigned local_gotno, gotsym, symtabno;
Elf32_Sym *symtab, *sym;
unsigned g;
got = si->plt_got;
local_gotno = si->mips_local_gotno;
gotsym = si->mips_gotsym;
symtabno = si->mips_symtabno;
symtab = si->symtab;
/*
* got[0] is address of lazy resolver function
* got[1] may be used for a GNU extension
* set it to a recognizable address in case someone calls it
* (should be _rtld_bind_start)
* FIXME: maybe this should be in a separate routine
*/
if ((si->flags & FLAG_LINKER) == 0) {
g = 0;
got[g++] = 0xdeadbeef;
if (got[g] & 0x80000000) {
got[g++] = 0xdeadfeed;
}
/*
* Relocate the local GOT entries need to be relocated
*/
for (; g < local_gotno; g++) {
got[g] += si->load_bias;
}
}
/* Now for the global GOT entries */
sym = symtab + gotsym;
got = si->plt_got + local_gotno;
for (g = gotsym; g < symtabno; g++, sym++, got++) {
const char* sym_name;
Elf32_Sym* s;
soinfo* lsi;
/* This is an undefined reference... try to locate it */
sym_name = si->strtab + sym->st_name;
s = soinfo_do_lookup(si, sym_name, &lsi, needed);
if (s == NULL) {
/* We only allow an undefined symbol if this is a weak
reference.. */
s = &symtab[g];
if (ELF32_ST_BIND(s->st_info) != STB_WEAK) {
DL_ERR("cannot locate \"%s\"...", sym_name);
return -1;
}
*got = 0;
}
else {
/* FIXME: is this sufficient?
* For reference see NetBSD link loader
* http://cvsweb.netbsd.org/bsdweb.cgi/src/libexec/ld.elf_so/arch/mips/mips_reloc.c?rev=1.53&content-type=text/x-cvsweb-markup
*/
*got = lsi->load_bias + s->st_value;
}
}
return 0;
}
#endif
void soinfo::CallArray(const char* array_name UNUSED, linker_function_t* functions, size_t count, bool reverse) {
if (functions == NULL) {
return;
}
TRACE("[ Calling %s (size %d) @ %p for '%s' ]", array_name, count, functions, name);
int begin = reverse ? (count - 1) : 0;
int end = reverse ? -1 : count;
int step = reverse ? -1 : 1;
for (int i = begin; i != end; i += step) {
TRACE("[ %s[%d] == %p ]", array_name, i, functions[i]);
CallFunction("function", functions[i]);
}
TRACE("[ Done calling %s for '%s' ]", array_name, name);
}
void soinfo::CallFunction(const char* function_name UNUSED, linker_function_t function) {
if (function == NULL || reinterpret_cast<uintptr_t>(function) == static_cast<uintptr_t>(-1)) {
return;
}
TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name);
function();
TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name);
// The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures
// are still writable. This happens with our debug malloc (see http://b/7941716).
set_soinfo_pool_protection(PROT_READ | PROT_WRITE);
}
void soinfo::CallPreInitConstructors() {
// DT_PREINIT_ARRAY functions are called before any other constructors for executables,
// but ignored in a shared library.
CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false);
}
void soinfo::CallConstructors() {
if (constructors_called) {
return;
}
// We set constructors_called before actually calling the constructors, otherwise it doesn't
// protect against recursive constructor calls. One simple example of constructor recursion
// is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so:
// 1. The program depends on libc, so libc's constructor is called here.
// 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so.
// 3. dlopen() calls the constructors on the newly created
// soinfo for libc_malloc_debug_leak.so.
// 4. The debug .so depends on libc, so CallConstructors is
// called again with the libc soinfo. If it doesn't trigger the early-
// out above, the libc constructor will be called again (recursively!).
constructors_called = true;
if ((flags & FLAG_EXE) == 0 && preinit_array != NULL) {
// The GNU dynamic linker silently ignores these, but we warn the developer.
PRINT("\"%s\": ignoring %d-entry DT_PREINIT_ARRAY in shared library!",
name, preinit_array_count);
}
if (dynamic != NULL) {
for (Elf32_Dyn* d = dynamic; d->d_tag != DT_NULL; ++d) {
if (d->d_tag == DT_NEEDED) {
const char* library_name = strtab + d->d_un.d_val;
TRACE("\"%s\": calling constructors in DT_NEEDED \"%s\"", name, library_name);
find_loaded_library(library_name)->CallConstructors();
}
}
}
TRACE("\"%s\": calling constructors", name);
// DT_INIT should be called before DT_INIT_ARRAY if both are present.
CallFunction("DT_INIT", init_func);
CallArray("DT_INIT_ARRAY", init_array, init_array_count, false);
}
void soinfo::CallDestructors() {
TRACE("\"%s\": calling destructors", name);
// DT_FINI_ARRAY must be parsed in reverse order.
CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true);
// DT_FINI should be called after DT_FINI_ARRAY if both are present.
CallFunction("DT_FINI", fini_func);
}
/* Force any of the closed stdin, stdout and stderr to be associated with
/dev/null. */
static int nullify_closed_stdio() {
int dev_null, i, status;
int return_value = 0;
dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR));
if (dev_null < 0) {
DL_ERR("cannot open /dev/null: %s", strerror(errno));
return -1;
}
TRACE("[ Opened /dev/null file-descriptor=%d]", dev_null);
/* If any of the stdio file descriptors is valid and not associated
with /dev/null, dup /dev/null to it. */
for (i = 0; i < 3; i++) {
/* If it is /dev/null already, we are done. */
if (i == dev_null) {
continue;
}
TRACE("[ Nullifying stdio file descriptor %d]", i);
status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL));
/* If file is opened, we are good. */
if (status != -1) {
continue;
}
/* The only error we allow is that the file descriptor does not
exist, in which case we dup /dev/null to it. */
if (errno != EBADF) {
DL_ERR("fcntl failed: %s", strerror(errno));
return_value = -1;
continue;
}
/* Try dupping /dev/null to this stdio file descriptor and
repeat if there is a signal. Note that any errors in closing
the stdio descriptor are lost. */
status = TEMP_FAILURE_RETRY(dup2(dev_null, i));
if (status < 0) {
DL_ERR("dup2 failed: %s", strerror(errno));
return_value = -1;
continue;
}
}
/* If /dev/null is not one of the stdio file descriptors, close it. */
if (dev_null > 2) {
TRACE("[ Closing /dev/null file-descriptor=%d]", dev_null);
status = TEMP_FAILURE_RETRY(close(dev_null));
if (status == -1) {
DL_ERR("close failed: %s", strerror(errno));
return_value = -1;
}
}
return return_value;
}
static bool soinfo_link_image(soinfo* si) {
/* "base" might wrap around UINT32_MAX. */
Elf32_Addr base = si->load_bias;
const Elf32_Phdr *phdr = si->phdr;
int phnum = si->phnum;
bool relocating_linker = (si->flags & FLAG_LINKER) != 0;
/* We can't debug anything until the linker is relocated */
if (!relocating_linker) {
INFO("[ linking %s ]", si->name);
DEBUG("si->base = 0x%08x si->flags = 0x%08x", si->base, si->flags);
}
/* Extract dynamic section */
size_t dynamic_count;
Elf32_Word dynamic_flags;
phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic,
&dynamic_count, &dynamic_flags);
if (si->dynamic == NULL) {
if (!relocating_linker) {
DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name);
}
return false;
} else {
if (!relocating_linker) {
DEBUG("dynamic = %p", si->dynamic);
}
}
#ifdef ANDROID_ARM_LINKER
(void) phdr_table_get_arm_exidx(phdr, phnum, base,
&si->ARM_exidx, &si->ARM_exidx_count);
#endif
// Extract useful information from dynamic section.
uint32_t needed_count = 0;
for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) {
DEBUG("d = %p, d[0](tag) = 0x%08x d[1](val) = 0x%08x", d, d->d_tag, d->d_un.d_val);
switch(d->d_tag){
case DT_HASH:
si->nbucket = ((unsigned *) (base + d->d_un.d_ptr))[0];
si->nchain = ((unsigned *) (base + d->d_un.d_ptr))[1];
si->bucket = (unsigned *) (base + d->d_un.d_ptr + 8);
si->chain = (unsigned *) (base + d->d_un.d_ptr + 8 + si->nbucket * 4);
break;
case DT_STRTAB:
si->strtab = (const char *) (base + d->d_un.d_ptr);
break;
case DT_SYMTAB:
si->symtab = (Elf32_Sym *) (base + d->d_un.d_ptr);
break;
case DT_PLTREL:
if (d->d_un.d_val != DT_REL) {
DL_ERR("unsupported DT_RELA in \"%s\"", si->name);
return false;
}
break;
case DT_JMPREL:
si->plt_rel = (Elf32_Rel*) (base + d->d_un.d_ptr);
break;
case DT_PLTRELSZ:
si->plt_rel_count = d->d_un.d_val / sizeof(Elf32_Rel);
break;
case DT_REL:
si->rel = (Elf32_Rel*) (base + d->d_un.d_ptr);
break;
case DT_RELSZ:
si->rel_count = d->d_un.d_val / sizeof(Elf32_Rel);
break;
case DT_PLTGOT:
/* Save this in case we decide to do lazy binding. We don't yet. */
si->plt_got = (unsigned *)(base + d->d_un.d_ptr);
break;
case DT_DEBUG:
// Set the DT_DEBUG entry to the address of _r_debug for GDB
// if the dynamic table is writable
if ((dynamic_flags & PF_W) != 0) {
d->d_un.d_val = (int) &_r_debug;
}
break;
case DT_RELA:
DL_ERR("unsupported DT_RELA in \"%s\"", si->name);
return false;
case DT_INIT:
si->init_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr);
DEBUG("%s constructors (DT_INIT) found at %p", si->name, si->init_func);
break;
case DT_FINI:
si->fini_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr);
DEBUG("%s destructors (DT_FINI) found at %p", si->name, si->fini_func);
break;
case DT_INIT_ARRAY:
si->init_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr);
DEBUG("%s constructors (DT_INIT_ARRAY) found at %p", si->name, si->init_array);
break;
case DT_INIT_ARRAYSZ:
si->init_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr);
break;
case DT_FINI_ARRAY:
si->fini_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr);
DEBUG("%s destructors (DT_FINI_ARRAY) found at %p", si->name, si->fini_array);
break;
case DT_FINI_ARRAYSZ:
si->fini_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr);
break;
case DT_PREINIT_ARRAY:
si->preinit_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr);
DEBUG("%s constructors (DT_PREINIT_ARRAY) found at %p", si->name, si->preinit_array);
break;
case DT_PREINIT_ARRAYSZ:
si->preinit_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr);
break;
case DT_TEXTREL:
si->has_text_relocations = true;
break;
case DT_SYMBOLIC:
si->has_DT_SYMBOLIC = true;
break;
case DT_NEEDED:
++needed_count;
break;
#if defined DT_FLAGS
// TODO: why is DT_FLAGS not defined?
case DT_FLAGS:
if (d->d_un.d_val & DF_TEXTREL) {
si->has_text_relocations = true;
}
if (d->d_un.d_val & DF_SYMBOLIC) {
si->has_DT_SYMBOLIC = true;
}
break;
#endif
#if defined(ANDROID_MIPS_LINKER)
case DT_STRSZ:
case DT_SYMENT:
case DT_RELENT:
break;
case DT_MIPS_RLD_MAP:
// Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB.
{
r_debug** dp = (r_debug**) d->d_un.d_ptr;
*dp = &_r_debug;
}
break;
case DT_MIPS_RLD_VERSION:
case DT_MIPS_FLAGS:
case DT_MIPS_BASE_ADDRESS:
case DT_MIPS_UNREFEXTNO:
break;
case DT_MIPS_SYMTABNO:
si->mips_symtabno = d->d_un.d_val;
break;
case DT_MIPS_LOCAL_GOTNO:
si->mips_local_gotno = d->d_un.d_val;
break;
case DT_MIPS_GOTSYM:
si->mips_gotsym = d->d_un.d_val;
break;
default:
DEBUG("Unused DT entry: type 0x%08x arg 0x%08x", d->d_tag, d->d_un.d_val);
break;
#endif
}
}
DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p",
si->base, si->strtab, si->symtab);
// Sanity checks.
if (relocating_linker && needed_count != 0) {
DL_ERR("linker cannot have DT_NEEDED dependencies on other libraries");
return false;
}
if (si->nbucket == 0) {
DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name);
return false;
}
if (si->strtab == 0) {
DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name);
return false;
}
if (si->symtab == 0) {
DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name);
return false;
}
/* if this is the main executable, then load all of the preloads now */
if (si->flags & FLAG_EXE) {
memset(gLdPreloads, 0, sizeof(gLdPreloads));
for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) {
soinfo* lsi = find_library(gLdPreloadNames[i]);
if (lsi == NULL) {
strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf));
DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s",
gLdPreloadNames[i], si->name, tmp_err_buf);
return false;
}
gLdPreloads[i] = lsi;
}
}
soinfo** needed = (soinfo**) alloca((1 + needed_count) * sizeof(soinfo*));
soinfo** pneeded = needed;
for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) {
if (d->d_tag == DT_NEEDED) {
const char* library_name = si->strtab + d->d_un.d_val;
DEBUG("%s needs %s", si->name, library_name);
soinfo* lsi = find_library(library_name);
if (lsi == NULL) {
strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf));
DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s",
library_name, si->name, tmp_err_buf);
return false;
}
*pneeded++ = lsi;
}
}
*pneeded = NULL;
if (si->has_text_relocations) {
/* Unprotect the segments, i.e. make them writable, to allow
* text relocations to work properly. We will later call
* phdr_table_protect_segments() after all of them are applied
* and all constructors are run.
*/
if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) {
DL_ERR("can't unprotect loadable segments for \"%s\": %s",
si->name, strerror(errno));
return false;
}
}
if (si->plt_rel != NULL) {
DEBUG("[ relocating %s plt ]", si->name );
if (soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) {
return false;
}
}
if (si->rel != NULL) {
DEBUG("[ relocating %s ]", si->name );
if (soinfo_relocate(si, si->rel, si->rel_count, needed)) {
return false;
}
}
#ifdef ANDROID_MIPS_LINKER
if (mips_relocate_got(si, needed)) {
return false;
}
#endif
si->flags |= FLAG_LINKED;
DEBUG("[ finished linking %s ]", si->name);
if (si->has_text_relocations) {
/* All relocations are done, we can protect our segments back to
* read-only. */
if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) {
DL_ERR("can't protect segments for \"%s\": %s",
si->name, strerror(errno));
return false;
}
}
/* We can also turn on GNU RELRO protection */
if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) {
DL_ERR("can't enable GNU RELRO protection for \"%s\": %s",
si->name, strerror(errno));
return false;
}
notify_gdb_of_load(si);
return true;
}
/*
* This code is called after the linker has linked itself and
* fixed it's own GOT. It is safe to make references to externs
* and other non-local data at this point.
*/
static Elf32_Addr __linker_init_post_relocation(KernelArgumentBlock& args, Elf32_Addr linker_base) {
/* NOTE: we store the args pointer on a special location
* of the temporary TLS area in order to pass it to
* the C Library's runtime initializer.
*
* The initializer must clear the slot and reset the TLS
* to point to a different location to ensure that no other
* shared library constructor can access it.
*/
__libc_init_tls(args);
#if TIMING
struct timeval t0, t1;
gettimeofday(&t0, 0);
#endif
// Initialize environment functions, and get to the ELF aux vectors table.
linker_env_init(args);
// If this is a setuid/setgid program, close the security hole described in
// ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc
if (get_AT_SECURE()) {
nullify_closed_stdio();
}
debuggerd_init();
// Get a few environment variables.
const char* LD_DEBUG = linker_env_get("LD_DEBUG");
if (LD_DEBUG != NULL) {
gLdDebugVerbosity = atoi(LD_DEBUG);
}
// Normally, these are cleaned by linker_env_init, but the test
// doesn't cost us anything.
const char* ldpath_env = NULL;
const char* ldpreload_env = NULL;
if (!get_AT_SECURE()) {
ldpath_env = linker_env_get("LD_LIBRARY_PATH");
ldpreload_env = linker_env_get("LD_PRELOAD");
}
INFO("[ android linker & debugger ]");
soinfo* si = soinfo_alloc(args.argv[0]);
if (si == NULL) {
exit(EXIT_FAILURE);
}
/* bootstrap the link map, the main exe always needs to be first */
si->flags |= FLAG_EXE;
link_map_t* map = &(si->link_map);
map->l_addr = 0;
map->l_name = args.argv[0];
map->l_prev = NULL;
map->l_next = NULL;
_r_debug.r_map = map;
r_debug_tail = map;
/* gdb expects the linker to be in the debug shared object list.
* Without this, gdb has trouble locating the linker's ".text"
* and ".plt" sections. Gdb could also potentially use this to
* relocate the offset of our exported 'rtld_db_dlactivity' symbol.
* Don't use soinfo_alloc(), because the linker shouldn't
* be on the soinfo list.
*/
{
static soinfo linker_soinfo;
strlcpy(linker_soinfo.name, "/system/bin/linker", sizeof(linker_soinfo.name));
linker_soinfo.flags = 0;
linker_soinfo.base = linker_base;
/*
* Set the dynamic field in the link map otherwise gdb will complain with
* the following:
* warning: .dynamic section for "/system/bin/linker" is not at the
* expected address (wrong library or version mismatch?)
*/
Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base;
Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_base + elf_hdr->e_phoff);
phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base,
&linker_soinfo.dynamic, NULL, NULL);
insert_soinfo_into_debug_map(&linker_soinfo);
}
// Extract information passed from the kernel.
si->phdr = reinterpret_cast<Elf32_Phdr*>(args.getauxval(AT_PHDR));
si->phnum = args.getauxval(AT_PHNUM);
si->entry = args.getauxval(AT_ENTRY);
/* Compute the value of si->base. We can't rely on the fact that
* the first entry is the PHDR because this will not be true
* for certain executables (e.g. some in the NDK unit test suite)
*/
si->base = 0;
si->size = phdr_table_get_load_size(si->phdr, si->phnum);
si->load_bias = 0;
for (size_t i = 0; i < si->phnum; ++i) {
if (si->phdr[i].p_type == PT_PHDR) {
si->load_bias = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_vaddr;
si->base = reinterpret_cast<Elf32_Addr>(si->phdr) - si->phdr[i].p_offset;
break;
}
}
si->dynamic = NULL;
si->ref_count = 1;
// Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid).
parse_LD_LIBRARY_PATH(ldpath_env);
parse_LD_PRELOAD(ldpreload_env);
somain = si;
if (!soinfo_link_image(si)) {
__libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer());
exit(EXIT_FAILURE);
}
si->CallPreInitConstructors();
for (size_t i = 0; gLdPreloads[i] != NULL; ++i) {
gLdPreloads[i]->CallConstructors();
}
/* After the link_image, the si->load_bias is initialized.
* For so lib, the map->l_addr will be updated in notify_gdb_of_load.
* We need to update this value for so exe here. So Unwind_Backtrace
* for some arch like x86 could work correctly within so exe.
*/
map->l_addr = si->load_bias;
si->CallConstructors();
#if TIMING
gettimeofday(&t1,NULL);
PRINT("LINKER TIME: %s: %d microseconds", args.argv[0], (int) (
(((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) -
(((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec)
));
#endif
#if STATS
PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", args.argv[0],
linker_stats.count[kRelocAbsolute],
linker_stats.count[kRelocRelative],
linker_stats.count[kRelocCopy],
linker_stats.count[kRelocSymbol]);
#endif
#if COUNT_PAGES
{
unsigned n;
unsigned i;
unsigned count = 0;
for (n = 0; n < 4096; n++) {
if (bitmask[n]) {
unsigned x = bitmask[n];
for (i = 0; i < 8; i++) {
if (x & 1) {
count++;
}
x >>= 1;
}
}
}
PRINT("PAGES MODIFIED: %s: %d (%dKB)", args.argv[0], count, count * 4);
}
#endif
#if TIMING || STATS || COUNT_PAGES
fflush(stdout);
#endif
TRACE("[ Ready to execute '%s' @ 0x%08x ]", si->name, si->entry);
return si->entry;
}
/* Compute the load-bias of an existing executable. This shall only
* be used to compute the load bias of an executable or shared library
* that was loaded by the kernel itself.
*
* Input:
* elf -> address of ELF header, assumed to be at the start of the file.
* Return:
* load bias, i.e. add the value of any p_vaddr in the file to get
* the corresponding address in memory.
*/
static Elf32_Addr get_elf_exec_load_bias(const Elf32_Ehdr* elf) {
Elf32_Addr offset = elf->e_phoff;
const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset);
const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum;
for (const Elf32_Phdr* phdr = phdr_table; phdr < phdr_end; phdr++) {
if (phdr->p_type == PT_LOAD) {
return reinterpret_cast<Elf32_Addr>(elf) + phdr->p_offset - phdr->p_vaddr;
}
}
return 0;
}
/*
* This is the entry point for the linker, called from begin.S. This
* method is responsible for fixing the linker's own relocations, and
* then calling __linker_init_post_relocation().
*
* Because this method is called before the linker has fixed it's own
* relocations, any attempt to reference an extern variable, extern
* function, or other GOT reference will generate a segfault.
*/
extern "C" Elf32_Addr __linker_init(void* raw_args) {
KernelArgumentBlock args(raw_args);
Elf32_Addr linker_addr = args.getauxval(AT_BASE);
Elf32_Ehdr* elf_hdr = (Elf32_Ehdr*) linker_addr;
Elf32_Phdr* phdr = (Elf32_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff);
soinfo linker_so;
memset(&linker_so, 0, sizeof(soinfo));
linker_so.base = linker_addr;
linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum);
linker_so.load_bias = get_elf_exec_load_bias(elf_hdr);
linker_so.dynamic = NULL;
linker_so.phdr = phdr;
linker_so.phnum = elf_hdr->e_phnum;
linker_so.flags |= FLAG_LINKER;
if (!soinfo_link_image(&linker_so)) {
// It would be nice to print an error message, but if the linker
// can't link itself, there's no guarantee that we'll be able to
// call write() (because it involves a GOT reference).
//
// This situation should never occur unless the linker itself
// is corrupt.
exit(EXIT_FAILURE);
}
// We have successfully fixed our own relocations. It's safe to run
// the main part of the linker now.
args.abort_message_ptr = &gAbortMessage;
Elf32_Addr start_address = __linker_init_post_relocation(args, linker_addr);
set_soinfo_pool_protection(PROT_READ);
// Return the address that the calling assembly stub should jump to.
return start_address;
}
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