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bionic/linker/linker.c

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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 <linux/auxvec.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <dlfcn.h>
#include <sys/stat.h>
#include <pthread.h>
#include <sys/mman.h>
#include <sys/atomics.h>
/* special private C library header - see Android.mk */
#include <bionic_tls.h>
#include "linker.h"
#include "linker_debug.h"
#include "linker_environ.h"
#include "linker_format.h"
#include "linker_phdr.h"
#define ALLOW_SYMBOLS_FROM_MAIN 1
#define SO_MAX 128
/* 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
* - linker hardcodes PAGE_SIZE and PAGE_MASK because the kernel
* headers provide versions that are negative...
* - allocate space for soinfo structs dynamically instead of
* having a hard limit (64)
*/
static int soinfo_link_image(soinfo *si, unsigned wr_offset);
static int socount = 0;
static soinfo sopool[SO_MAX];
static soinfo *freelist = NULL;
static soinfo *solist = &libdl_info;
static soinfo *sonext = &libdl_info;
#if ALLOW_SYMBOLS_FROM_MAIN
static soinfo *somain; /* main process, always the one after libdl_info */
#endif
static inline int validate_soinfo(soinfo *si)
{
return (si >= sopool && si < sopool + SO_MAX) ||
si == &libdl_info;
}
static char ldpaths_buf[LDPATH_BUFSIZE];
static const char *ldpaths[LDPATH_MAX + 1];
static char ldpreloads_buf[LDPRELOAD_BUFSIZE];
static const char *ldpreload_names[LDPRELOAD_MAX + 1];
static soinfo *preloads[LDPRELOAD_MAX + 1];
#if LINKER_DEBUG
int debug_verbosity;
#endif
static int pid;
/* This boolean is set if the program being loaded is setuid */
static int program_is_setuid;
#if STATS
struct _link_stats linker_stats;
#endif
#if COUNT_PAGES
unsigned bitmask[4096];
#endif
#define HOODLUM(name, ret, ...) \
ret name __VA_ARGS__ \
{ \
char errstr[] = "ERROR: " #name " called from the dynamic linker!\n"; \
write(2, errstr, sizeof(errstr)); \
abort(); \
}
HOODLUM(malloc, void *, (size_t size));
HOODLUM(free, void, (void *ptr));
HOODLUM(realloc, void *, (void *ptr, size_t size));
HOODLUM(calloc, void *, (size_t cnt, size_t size));
static char tmp_err_buf[768];
static char __linker_dl_err_buf[768];
#define DL_ERR(fmt, x...) \
do { \
format_buffer(__linker_dl_err_buf, sizeof(__linker_dl_err_buf), \
"%s[%d]: " fmt, __func__, __LINE__, ##x); \
ERROR(fmt "\n", ##x); \
} while(0)
const char *linker_get_error(void)
{
return (const char *)&__linker_dl_err_buf[0];
}
/*
* This function is an empty stub where GDB locates a breakpoint to get notified
* about linker activity.
*/
extern void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(void);
static struct r_debug _r_debug = {1, NULL, &rtld_db_dlactivity,
RT_CONSISTENT, 0};
static struct link_map *r_debug_tail = 0;
static pthread_mutex_t _r_debug_lock = PTHREAD_MUTEX_INITIALIZER;
static void insert_soinfo_into_debug_map(soinfo * info)
{
struct link_map * map;
/* Copy the necessary fields into the debug structure.
*/
map = &(info->linkmap);
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)
{
struct link_map * map = &(info->linkmap);
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;
}
void notify_gdb_of_load(soinfo * info)
{
if (info->flags & FLAG_EXE) {
// GDB already knows about the main executable
return;
}
pthread_mutex_lock(&_r_debug_lock);
_r_debug.r_state = RT_ADD;
rtld_db_dlactivity();
insert_soinfo_into_debug_map(info);
_r_debug.r_state = RT_CONSISTENT;
rtld_db_dlactivity();
pthread_mutex_unlock(&_r_debug_lock);
}
void notify_gdb_of_unload(soinfo * info)
{
if (info->flags & FLAG_EXE) {
// GDB already knows about the main executable
return;
}
pthread_mutex_lock(&_r_debug_lock);
_r_debug.r_state = RT_DELETE;
rtld_db_dlactivity();
remove_soinfo_from_debug_map(info);
_r_debug.r_state = RT_CONSISTENT;
rtld_db_dlactivity();
pthread_mutex_unlock(&_r_debug_lock);
}
void notify_gdb_of_libraries()
{
_r_debug.r_state = RT_ADD;
rtld_db_dlactivity();
_r_debug.r_state = RT_CONSISTENT;
rtld_db_dlactivity();
}
static soinfo *soinfo_alloc(const char *name)
{
soinfo *si;
if(strlen(name) >= SOINFO_NAME_LEN) {
DL_ERR("%5d library name %s too long", pid, name);
return NULL;
}
/* The freelist is populated when we call soinfo_free(), which in turn is
done only by dlclose(), which is not likely to be used.
*/
if (!freelist) {
if(socount == SO_MAX) {
DL_ERR("%5d too many libraries when loading %s", pid, name);
return NULL;
}
freelist = sopool + socount++;
freelist->next = NULL;
}
si = freelist;
freelist = freelist->next;
/* Make sure we get a clean block of soinfo */
memset(si, 0, sizeof(soinfo));
strlcpy((char*) si->name, name, sizeof(si->name));
sonext->next = si;
si->next = NULL;
si->refcount = 0;
sonext = si;
TRACE("%5d name %s: allocated soinfo @ %p\n", pid, name, si);
return si;
}
static void soinfo_free(soinfo *si)
{
soinfo *prev = NULL, *trav;
TRACE("%5d name %s: freeing soinfo @ %p\n", pid, si->name, si);
for(trav = solist; trav != NULL; trav = trav->next){
if (trav == si)
break;
prev = trav;
}
if (trav == NULL) {
/* si was not ni solist */
DL_ERR("%5d name %s is not in solist!", pid, 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 = freelist;
freelist = si;
}
const char *addr_to_name(unsigned addr)
{
soinfo *si;
for(si = solist; si != 0; si = si->next){
if((addr >= si->base) && (addr < (si->base + si->size))) {
return si->name;
}
}
return "";
}
/* 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.c and libdl.so.
*/
#ifdef ANDROID_ARM_LINKER
_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)
/* 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)(struct dl_phdr_info *info, size_t size, void *data),
void *data)
{
soinfo *si;
struct dl_phdr_info dl_info;
int rv = 0;
for (si = solist; si != NULL; si = si->next) {
dl_info.dlpi_addr = si->linkmap.l_addr;
dl_info.dlpi_name = si->linkmap.l_name;
dl_info.dlpi_phdr = si->phdr;
dl_info.dlpi_phnum = si->phnum;
rv = cb(&dl_info, sizeof (struct 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 *s;
Elf32_Sym *symtab = si->symtab;
const char *strtab = si->strtab;
unsigned n;
TRACE_TYPE(LOOKUP, "%5d SEARCH %s in %s@0x%08x %08x %d\n", pid,
name, si->name, si->base, hash, hash % si->nbucket);
n = hash % si->nbucket;
for(n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]){
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, "%5d FOUND %s in %s (%08x) %d\n", pid,
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, Elf32_Addr *offset)
{
unsigned elf_hash = elfhash(name);
Elf32_Sym *s;
unsigned *d;
soinfo *lsi = si;
int i;
/* 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 ambigious 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)
goto done;
/* Next, look for it in the preloads list */
for(i = 0; preloads[i] != NULL; i++) {
lsi = preloads[i];
s = soinfo_elf_lookup(lsi, elf_hash, name);
if(s != NULL)
goto done;
}
for(d = si->dynamic; *d; d += 2) {
if(d[0] == DT_NEEDED){
lsi = (soinfo *)d[1];
if (!validate_soinfo(lsi)) {
DL_ERR("%5d bad DT_NEEDED pointer in %s",
pid, si->name);
return NULL;
}
DEBUG("%5d %s: looking up %s in %s\n",
pid, si->name, name, lsi->name);
s = soinfo_elf_lookup(lsi, elf_hash, name);
if (s != NULL)
goto done;
}
}
#if ALLOW_SYMBOLS_FROM_MAIN
/* If we are resolving relocations while dlopen()ing a library, it's OK for
* the library to resolve a symbol that's defined in the executable itself,
* although this is rare and is generally a bad idea.
*/
if (somain) {
lsi = somain;
DEBUG("%5d %s: looking up %s in executable %s\n",
pid, si->name, name, lsi->name);
s = soinfo_elf_lookup(lsi, elf_hash, name);
}
#endif
done:
if(s != NULL) {
TRACE_TYPE(LOOKUP, "%5d si %s sym %s s->st_value = 0x%08x, "
"found in %s, base = 0x%08x, load bias = 0x%08x\n",
pid, si->name, name, s->st_value,
lsi->name, lsi->base, lsi->load_bias);
*offset = lsi->load_bias;
return s;
}
return NULL;
}
/* This is used by dl_sym(). It performs symbol lookup only within the
specified soinfo object and not in any of its dependencies.
*/
Elf32_Sym *soinfo_lookup(soinfo *si, const char *name)
{
return soinfo_elf_lookup(si, elfhash(name), name);
}
/* This is used by dl_sym(). It performs a global symbol lookup.
*/
Elf32_Sym *lookup(const char *name, soinfo **found, soinfo *start)
{
unsigned elf_hash = elfhash(name);
Elf32_Sym *s = NULL;
soinfo *si;
if(start == NULL) {
start = solist;
}
for(si = start; (s == NULL) && (si != NULL); si = si->next)
{
if(si->flags & FLAG_ERROR)
continue;
s = soinfo_elf_lookup(si, elf_hash, name);
if (s != NULL) {
*found = si;
break;
}
}
if(s != NULL) {
TRACE_TYPE(LOOKUP, "%5d %s s->st_value = 0x%08x, "
"si->base = 0x%08x\n", pid, name, s->st_value, si->base);
return s;
}
return NULL;
}
soinfo *find_containing_library(const void *addr)
{
soinfo *si;
for(si = solist; si != NULL; si = si->next)
{
if((unsigned)addr >= si->base && (unsigned)addr - si->base < si->size) {
return si;
}
}
return NULL;
}
Elf32_Sym *soinfo_find_symbol(soinfo* si, const void *addr)
{
unsigned int i;
unsigned soaddr = (unsigned)addr - si->base;
/* Search the library's symbol table for any defined symbol which
* contains this address */
for(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;
unsigned n;
for(n = 0; n < si->nchain; n++) {
TRACE("%5d %04d> %08x: %02x %04x %08x %08x %s\n", pid, n, s,
s->st_info, s->st_shndx, s->st_value, s->st_size,
si->strtab + s->st_name);
s++;
}
}
#endif
static const char * const sopaths[] = {
"/vendor/lib",
"/system/lib",
0
};
static int _open_lib(const char *name)
{
int fd;
struct stat filestat;
if ((stat(name, &filestat) >= 0) && S_ISREG(filestat.st_mode)) {
if ((fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY))) >= 0)
return fd;
}
return -1;
}
static int open_library(const char *name)
{
int fd;
char buf[512];
const char * const*path;
int n;
TRACE("[ %5d opening %s ]\n", pid, name);
if(name == 0) return -1;
if(strlen(name) > 256) return -1;
if ((name[0] == '/') && ((fd = _open_lib(name)) >= 0))
return fd;
for (path = ldpaths; *path; path++) {
n = format_buffer(buf, sizeof(buf), "%s/%s", *path, name);
if (n < 0 || n >= (int)sizeof(buf)) {
WARN("Ignoring very long library path: %s/%s\n", *path, name);
continue;
}
if ((fd = _open_lib(buf)) >= 0)
return fd;
}
for (path = sopaths; *path; path++) {
n = format_buffer(buf, sizeof(buf), "%s/%s", *path, name);
if (n < 0 || n >= (int)sizeof(buf)) {
WARN("Ignoring very long library path: %s/%s\n", *path, name);
continue;
}
if ((fd = _open_lib(buf)) >= 0)
return fd;
}
return -1;
}
typedef struct {
long mmap_addr;
char tag[4]; /* 'P', 'R', 'E', ' ' */
} prelink_info_t;
/* Returns the requested base address if the library is prelinked,
* and 0 otherwise. */
static unsigned long
is_prelinked(int fd, const char *name)
{
off_t sz;
prelink_info_t info;
sz = lseek(fd, -sizeof(prelink_info_t), SEEK_END);
if (sz < 0) {
DL_ERR("lseek() failed!");
return 0;
}
if (TEMP_FAILURE_RETRY(read(fd, &info, sizeof(info)) != sizeof(info))) {
WARN("Could not read prelink_info_t structure for `%s`\n", name);
return 0;
}
if (memcmp(info.tag, "PRE ", 4)) {
WARN("`%s` is not a prelinked library\n", name);
return 0;
}
return (unsigned long)info.mmap_addr;
}
/* verify_elf_header
* Verifies the content of an ELF header.
*
* Args:
*
* Returns:
* 0 on success
* -1 if no valid ELF object is found @ base.
*/
static int
verify_elf_header(const Elf32_Ehdr* hdr)
{
if (hdr->e_ident[EI_MAG0] != ELFMAG0) return -1;
if (hdr->e_ident[EI_MAG1] != ELFMAG1) return -1;
if (hdr->e_ident[EI_MAG2] != ELFMAG2) return -1;
if (hdr->e_ident[EI_MAG3] != ELFMAG3) return -1;
/* TODO: Should we verify anything else in the header? */
#ifdef ANDROID_ARM_LINKER
if (hdr->e_machine != EM_ARM) return -1;
#elif defined(ANDROID_X86_LINKER)
if (hdr->e_machine != EM_386) return -1;
#endif
return 0;
}
static soinfo *
load_library(const char *name)
{
int fd = open_library(name);
int ret, cnt;
unsigned ext_sz;
unsigned req_base;
const char *bname;
struct stat sb;
soinfo *si = NULL;
Elf32_Ehdr header[1];
int phdr_count;
void* phdr_mmap = NULL;
Elf32_Addr phdr_size;
const Elf32_Phdr* phdr_table;
void* load_start = NULL;
Elf32_Addr load_size = 0;
Elf32_Addr load_bias = 0;
if (fd == -1) {
DL_ERR("Library '%s' not found", name);
return NULL;
}
/* Read the ELF header first */
ret = TEMP_FAILURE_RETRY(read(fd, (void*)header, sizeof(header)));
if (ret < 0) {
DL_ERR("%5d can't read file %s: %s", pid, name, strerror(errno));
goto fail;
}
if (ret != (int)sizeof(header)) {
DL_ERR("%5d too small to be an ELF executable: %s", pid, name);
goto fail;
}
if (verify_elf_header(header) < 0) {
DL_ERR("%5d not a valid ELF executable: %s", pid, name);
goto fail;
}
/* Then read the program header table */
ret = phdr_table_load(fd, header->e_phoff, header->e_phnum,
&phdr_mmap, &phdr_size, &phdr_table);
if (ret < 0) {
DL_ERR("%5d can't load program header table: %s: %s", pid,
name, strerror(errno));
goto fail;
}
phdr_count = header->e_phnum;
/* Get the load extents and the prelinked load address, if any */
ext_sz = phdr_table_get_load_size(phdr_table, phdr_count);
if (ext_sz == 0) {
DL_ERR("%5d no loadable segments in file: %s", pid, name);
goto fail;
}
req_base = (unsigned) is_prelinked(fd, name);
if (req_base == (unsigned)-1) {
DL_ERR("%5d can't read end of library: %s: %s", pid, name,
strerror(errno));
goto fail;
}
if (req_base != 0) {
TRACE("[ %5d - Prelinked library '%s' requesting base @ 0x%08x ]\n",
pid, name, req_base);
} else {
TRACE("[ %5d - Non-prelinked library '%s' found. ]\n", pid, name);
}
TRACE("[ %5d - '%s' (%s) wants base=0x%08x sz=0x%08x ]\n", pid, name,
(req_base ? "prelinked" : "not pre-linked"), req_base, ext_sz);
/* Now configure the soinfo struct where we'll store all of our data
* for the ELF object. If the loading fails, we waste the entry, but
* same thing would happen if we failed during linking. Configuring the
* soinfo struct here is a lot more convenient.
*/
bname = strrchr(name, '/');
si = soinfo_alloc(bname ? bname + 1 : name);
if (si == NULL)
goto fail;
/* Reserve address space for all loadable segments */
ret = phdr_table_reserve_memory(phdr_table,
phdr_count,
req_base,
&load_start,
&load_size,
&load_bias);
if (ret < 0) {
DL_ERR("%5d Can't reserve %d bytes from 0x%08x in address space for %s: %s",
pid, ext_sz, req_base, name, strerror(errno));
goto fail;
}
TRACE("[ %5d allocated memory for %s @ %p (0x%08x) ]\n",
pid, name, load_start, load_size);
/* Map all the segments in our address space with default protections */
ret = phdr_table_load_segments(phdr_table,
phdr_count,
load_start,
load_size,
load_bias,
fd);
if (ret < 0) {
DL_ERR("%5d Can't map loadable segments for %s: %s",
pid, name, strerror(errno));
goto fail;
}
/* Unprotect the segments, i.e. make them writable, to allow
* relocations to work properly. We will later call
* phdr_table_protect_segments() after all of them are applied
* and all constructors are run.
*/
ret = phdr_table_unprotect_segments(phdr_table,
phdr_count,
load_bias);
if (ret < 0) {
DL_ERR("%5d Can't unprotect loadable segments for %s: %s",
pid, name, strerror(errno));
goto fail;
}
si->base = (Elf32_Addr) load_start;
si->size = load_size;
si->load_bias = load_bias;
si->flags = 0;
si->entry = 0;
si->dynamic = (unsigned *)-1;
si->phnum = phdr_count;
si->phdr = phdr_table_get_loaded_phdr(phdr_table, phdr_count, load_bias);
if (si->phdr == NULL) {
DL_ERR("%5d Can't find loaded PHDR for %s",
pid, name);
goto fail;
}
phdr_table_unload(phdr_mmap, phdr_size);
close(fd);
return si;
fail:
if (si) soinfo_free(si);
if (phdr_mmap != NULL) {
phdr_table_unload(phdr_mmap, phdr_size);
}
close(fd);
return NULL;
}
static soinfo *
init_library(soinfo *si)
{
unsigned wr_offset = 0xffffffff;
/* At this point we know that whatever is loaded @ base is a valid ELF
* shared library whose segments are properly mapped in. */
TRACE("[ %5d init_library base=0x%08x sz=0x%08x name='%s') ]\n",
pid, si->base, si->size, si->name);
if(soinfo_link_image(si, wr_offset)) {
/* We failed to link. However, we can only restore libbase
** if no additional libraries have moved it since we updated it.
*/
munmap((void *)si->base, si->size);
return NULL;
}
return si;
}
soinfo *find_library(const char *name)
{
soinfo *si;
const char *bname;
#if ALLOW_SYMBOLS_FROM_MAIN
if (name == NULL)
return somain;
#else
if (name == NULL)
return NULL;
#endif
bname = strrchr(name, '/');
bname = bname ? bname + 1 : name;
for(si = solist; si != 0; si = si->next){
if(!strcmp(bname, si->name)) {
if(si->flags & FLAG_ERROR) {
DL_ERR("%5d '%s' failed to load previously", pid, bname);
return NULL;
}
if(si->flags & FLAG_LINKED) return si;
DL_ERR("OOPS: %5d recursive link to '%s'", pid, si->name);
return NULL;
}
}
TRACE("[ %5d '%s' has not been loaded yet. Locating...]\n", pid, name);
si = load_library(name);
if(si == NULL)
return NULL;
return init_library(si);
}
/* TODO:
* notify gdb of unload
* for non-prelinked libraries, find a way to decrement libbase
*/
static void call_destructors(soinfo *si);
unsigned soinfo_unload(soinfo *si)
{
unsigned *d;
if (si->refcount == 1) {
TRACE("%5d unloading '%s'\n", pid, si->name);
call_destructors(si);
/*
* Make sure that we undo the PT_GNU_RELRO protections we added
* in soinfo_link_image. This is needed to undo the DT_NEEDED hack below.
*/
if (phdr_table_unprotect_gnu_relro(si->phdr, si->phnum,
si->load_bias) < 0) {
DL_ERR("%5d %s: could not undo GNU_RELRO protections. "
"Expect a crash soon. errno=%d (%s)",
pid, si->name, errno, strerror(errno));
}
for(d = si->dynamic; *d; d += 2) {
if(d[0] == DT_NEEDED){
soinfo *lsi = (soinfo *)d[1];
// The next line will segfault if the we don't undo the
// PT_GNU_RELRO protections (see comments above and in
// soinfo_link_image().
d[1] = 0;
if (validate_soinfo(lsi)) {
TRACE("%5d %s needs to unload %s\n", pid,
si->name, lsi->name);
soinfo_unload(lsi);
}
else
DL_ERR("%5d %s: could not unload dependent library",
pid, si->name);
}
}
munmap((char *)si->base, si->size);
notify_gdb_of_unload(si);
soinfo_free(si);
si->refcount = 0;
}
else {
si->refcount--;
PRINT("%5d not unloading '%s', decrementing refcount to %d\n",
pid, si->name, si->refcount);
}
return si->refcount;
}
/* 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)
{
Elf32_Sym *symtab = si->symtab;
const char *strtab = si->strtab;
Elf32_Sym *s;
unsigned base;
Elf32_Addr offset;
Elf32_Rel *start = rel;
unsigned idx;
for (idx = 0; idx < count; ++idx) {
unsigned type = ELF32_R_TYPE(rel->r_info);
unsigned sym = ELF32_R_SYM(rel->r_info);
unsigned reloc = (unsigned)(rel->r_offset + si->load_bias);
unsigned sym_addr = 0;
char *sym_name = NULL;
DEBUG("%5d Processing '%s' relocation at index %d\n", pid,
si->name, idx);
if(sym != 0) {
sym_name = (char *)(strtab + symtab[sym].st_name);
s = soinfo_do_lookup(si, sym_name, &offset);
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("%5d cannot locate '%s'...\n", pid, sym_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 nominial 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. */
case R_ARM_NONE: /* Don't care. */
#elif defined(ANDROID_X86_LINKER)
case R_386_JUMP_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("%5d unknown weak reloc type %d @ %p (%d)\n",
pid, 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("%5d cannot locate '%s'...",
pid, strtab + symtab[sym].st_name);
return -1;
}
#endif
sym_addr = (unsigned)(s->st_value + offset);
}
COUNT_RELOC(RELOC_SYMBOL);
} 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_RELOC(RELOC_ABSOLUTE);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO JMP_SLOT %08x <- %08x %s\n", pid,
reloc, sym_addr, sym_name);
*((unsigned*)reloc) = sym_addr;
break;
case R_ARM_GLOB_DAT:
COUNT_RELOC(RELOC_ABSOLUTE);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO GLOB_DAT %08x <- %08x %s\n", pid,
reloc, sym_addr, sym_name);
*((unsigned*)reloc) = sym_addr;
break;
case R_ARM_ABS32:
COUNT_RELOC(RELOC_ABSOLUTE);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO ABS %08x <- %08x %s\n", pid,
reloc, sym_addr, sym_name);
*((unsigned*)reloc) += sym_addr;
break;
case R_ARM_REL32:
COUNT_RELOC(RELOC_RELATIVE);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO REL32 %08x <- %08x - %08x %s\n", pid,
reloc, sym_addr, rel->r_offset, sym_name);
*((unsigned*)reloc) += sym_addr - rel->r_offset;
break;
#elif defined(ANDROID_X86_LINKER)
case R_386_JUMP_SLOT:
COUNT_RELOC(RELOC_ABSOLUTE);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO JMP_SLOT %08x <- %08x %s\n", pid,
reloc, sym_addr, sym_name);
*((unsigned*)reloc) = sym_addr;
break;
case R_386_GLOB_DAT:
COUNT_RELOC(RELOC_ABSOLUTE);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO GLOB_DAT %08x <- %08x %s\n", pid,
reloc, sym_addr, sym_name);
*((unsigned*)reloc) = sym_addr;
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_RELOC(RELOC_RELATIVE);
MARK(rel->r_offset);
if(sym){
DL_ERR("%5d odd RELATIVE form...", pid);
return -1;
}
TRACE_TYPE(RELO, "%5d RELO RELATIVE %08x <- +%08x\n", pid,
reloc, si->base);
*((unsigned*)reloc) += si->base;
break;
#if defined(ANDROID_X86_LINKER)
case R_386_32:
COUNT_RELOC(RELOC_RELATIVE);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO R_386_32 %08x <- +%08x %s\n", pid,
reloc, sym_addr, sym_name);
*((unsigned *)reloc) += (unsigned)sym_addr;
break;
case R_386_PC32:
COUNT_RELOC(RELOC_RELATIVE);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO R_386_PC32 %08x <- "
"+%08x (%08x - %08x) %s\n", pid, reloc,
(sym_addr - reloc), sym_addr, reloc, sym_name);
*((unsigned *)reloc) += (unsigned)(sym_addr - reloc);
break;
#endif /* ANDROID_X86_LINKER */
#ifdef ANDROID_ARM_LINKER
case R_ARM_COPY:
COUNT_RELOC(RELOC_COPY);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "%5d RELO %08x <- %d @ %08x %s\n", pid,
reloc, s->st_size, sym_addr, sym_name);
memcpy((void*)reloc, (void*)sym_addr, s->st_size);
break;
case R_ARM_NONE:
break;
#endif /* ANDROID_ARM_LINKER */
default:
DL_ERR("%5d unknown reloc type %d @ %p (%d)",
pid, type, rel, (int) (rel - start));
return -1;
}
rel++;
}
return 0;
}
/* Please read the "Initialization and Termination functions" functions.
* of the linker design note in bionic/linker/README.TXT to understand
* what the following code is doing.
*
* The important things to remember are:
*
* DT_PREINIT_ARRAY must be called first for executables, and should
* not appear in shared libraries.
*
* DT_INIT should be called before DT_INIT_ARRAY if both are present
*
* DT_FINI should be called after DT_FINI_ARRAY if both are present
*
* DT_FINI_ARRAY must be parsed in reverse order.
*/
static void call_array(unsigned *ctor, int count, int reverse)
{
int n, inc = 1;
if (reverse) {
ctor += (count-1);
inc = -1;
}
for(n = count; n > 0; n--) {
TRACE("[ %5d Looking at %s *0x%08x == 0x%08x ]\n", pid,
reverse ? "dtor" : "ctor",
(unsigned)ctor, (unsigned)*ctor);
void (*func)() = (void (*)()) *ctor;
ctor += inc;
if(((int) func == 0) || ((int) func == -1)) continue;
TRACE("[ %5d Calling func @ 0x%08x ]\n", pid, (unsigned)func);
func();
}
}
void soinfo_call_constructors(soinfo *si)
{
if (si->constructors_called)
return;
// Set this 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 soinfo_call_constructors() with the newly created
// soinfo for libc_malloc_debug_leak.so.
// 4. The debug so depends on libc, so soinfo_call_constructors() is
// called again with the libc soinfo. If it doesn't trigger the early-
// out above, the libc constructor will be called again (recursively!).
si->constructors_called = 1;
if (si->flags & FLAG_EXE) {
TRACE("[ %5d Calling preinit_array @ 0x%08x [%d] for '%s' ]\n",
pid, (unsigned)si->preinit_array, si->preinit_array_count,
si->name);
call_array(si->preinit_array, si->preinit_array_count, 0);
TRACE("[ %5d Done calling preinit_array for '%s' ]\n", pid, si->name);
} else {
if (si->preinit_array) {
DL_ERR("%5d Shared library '%s' has a preinit_array table @ 0x%08x."
" This is INVALID.", pid, si->name,
(unsigned)si->preinit_array);
}
}
if (si->dynamic) {
unsigned *d;
for(d = si->dynamic; *d; d += 2) {
if(d[0] == DT_NEEDED){
soinfo* lsi = (soinfo *)d[1];
if (!validate_soinfo(lsi)) {
DL_ERR("%5d bad DT_NEEDED pointer in %s",
pid, si->name);
} else {
soinfo_call_constructors(lsi);
}
}
}
}
if (si->init_func) {
TRACE("[ %5d Calling init_func @ 0x%08x for '%s' ]\n", pid,
(unsigned)si->init_func, si->name);
si->init_func();
TRACE("[ %5d Done calling init_func for '%s' ]\n", pid, si->name);
}
if (si->init_array) {
TRACE("[ %5d Calling init_array @ 0x%08x [%d] for '%s' ]\n", pid,
(unsigned)si->init_array, si->init_array_count, si->name);
call_array(si->init_array, si->init_array_count, 0);
TRACE("[ %5d Done calling init_array for '%s' ]\n", pid, si->name);
}
}
static void call_destructors(soinfo *si)
{
if (si->fini_array) {
TRACE("[ %5d Calling fini_array @ 0x%08x [%d] for '%s' ]\n", pid,
(unsigned)si->fini_array, si->fini_array_count, si->name);
call_array(si->fini_array, si->fini_array_count, 1);
TRACE("[ %5d Done calling fini_array for '%s' ]\n", pid, si->name);
}
if (si->fini_func) {
TRACE("[ %5d Calling fini_func @ 0x%08x for '%s' ]\n", pid,
(unsigned)si->fini_func, si->name);
si->fini_func();
TRACE("[ %5d Done calling fini_func for '%s' ]\n", pid, si->name);
}
}
/* Force any of the closed stdin, stdout and stderr to be associated with
/dev/null. */
static int nullify_closed_stdio (void)
{
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.");
return -1;
}
TRACE("[ %5d Opened /dev/null file-descriptor=%d]\n", pid, 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("[ %5d Nullifying stdio file descriptor %d]\n", pid, i);
/* The man page of fcntl does not say that fcntl(..,F_GETFL)
can be interrupted but we do this just to be safe. */
do {
status = fcntl(i, F_GETFL);
} while (status < 0 && errno == EINTR);
/* If file is openned, we are good. */
if (status >= 0)
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("nullify_stdio: unhandled error %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. */
do {
status = dup2(dev_null, i);
} while (status < 0 && errno == EINTR);
if (status < 0) {
DL_ERR("nullify_stdio: dup2 error %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("[ %5d Closing /dev/null file-descriptor=%d]\n", pid, dev_null);
do {
status = close(dev_null);
} while (status < 0 && errno == EINTR);
if (status < 0) {
DL_ERR("nullify_stdio: close error %s", strerror(errno));
return_value = -1;
}
}
return return_value;
}
static int soinfo_link_image(soinfo *si, unsigned wr_offset)
{
unsigned *d;
/* "base" might wrap around UINT32_MAX. */
Elf32_Addr base = si->load_bias;
const Elf32_Phdr *phdr = si->phdr;
int phnum = si->phnum;
int relocating_linker = (si->flags & FLAG_LINKER) != 0;
/* We can't debug anything until the linker is relocated */
if (!relocating_linker) {
INFO("[ %5d linking %s ]\n", pid, si->name);
DEBUG("%5d si->base = 0x%08x si->flags = 0x%08x\n", pid,
si->base, si->flags);
}
/* Extract dynamic section */
si->dynamic = phdr_table_get_dynamic_section(phdr, phnum, base);
if (si->dynamic == NULL) {
if (!relocating_linker) {
DL_ERR("%5d missing PT_DYNAMIC?!", pid);
}
goto fail;
} else {
if (!relocating_linker) {
DEBUG("%5d dynamic = %p\n", pid, si->dynamic);
}
}
#ifdef ANDROID_ARM_LINKER
(void) phdr_table_get_arm_exidx(phdr, phnum, base,
&si->ARM_exidx, &si->ARM_exidx_count);
#endif
if (si->flags & (FLAG_EXE | FLAG_LINKER)) {
if (phdr_table_unprotect_segments(si->phdr,
si->phnum,
si->load_bias) < 0) {
/* We can't call DL_ERR if the linker's relocations haven't
* been performed yet */
if (!relocating_linker) {
DL_ERR("%5d Can't unprotect segments for %s: %s",
pid, si->name, strerror(errno));
}
goto fail;
}
}
/* extract useful information from dynamic section */
for(d = si->dynamic; *d; d++){
DEBUG("%5d d = %p, d[0] = 0x%08x d[1] = 0x%08x\n", pid, d, d[0], d[1]);
switch(*d++){
case DT_HASH:
si->nbucket = ((unsigned *) (base + *d))[0];
si->nchain = ((unsigned *) (base + *d))[1];
si->bucket = (unsigned *) (base + *d + 8);
si->chain = (unsigned *) (base + *d + 8 + si->nbucket * 4);
break;
case DT_STRTAB:
si->strtab = (const char *) (base + *d);
break;
case DT_SYMTAB:
si->symtab = (Elf32_Sym *) (base + *d);
break;
case DT_PLTREL:
if(*d != DT_REL) {
DL_ERR("DT_RELA not supported");
goto fail;
}
break;
case DT_JMPREL:
si->plt_rel = (Elf32_Rel*) (base + *d);
break;
case DT_PLTRELSZ:
si->plt_rel_count = *d / 8;
break;
case DT_REL:
si->rel = (Elf32_Rel*) (base + *d);
break;
case DT_RELSZ:
si->rel_count = *d / 8;
break;
case DT_PLTGOT:
/* Save this in case we decide to do lazy binding. We don't yet. */
si->plt_got = (unsigned *)(base + *d);
break;
case DT_DEBUG:
// Set the DT_DEBUG entry to the addres of _r_debug for GDB
*d = (int) &_r_debug;
break;
case DT_RELA:
DL_ERR("%5d DT_RELA not supported", pid);
goto fail;
case DT_INIT:
si->init_func = (void (*)(void))(base + *d);
DEBUG("%5d %s constructors (init func) found at %p\n",
pid, si->name, si->init_func);
break;
case DT_FINI:
si->fini_func = (void (*)(void))(base + *d);
DEBUG("%5d %s destructors (fini func) found at %p\n",
pid, si->name, si->fini_func);
break;
case DT_INIT_ARRAY:
si->init_array = (unsigned *)(base + *d);
DEBUG("%5d %s constructors (init_array) found at %p\n",
pid, si->name, si->init_array);
break;
case DT_INIT_ARRAYSZ:
si->init_array_count = ((unsigned)*d) / sizeof(Elf32_Addr);
break;
case DT_FINI_ARRAY:
si->fini_array = (unsigned *)(base + *d);
DEBUG("%5d %s destructors (fini_array) found at %p\n",
pid, si->name, si->fini_array);
break;
case DT_FINI_ARRAYSZ:
si->fini_array_count = ((unsigned)*d) / sizeof(Elf32_Addr);
break;
case DT_PREINIT_ARRAY:
si->preinit_array = (unsigned *)(base + *d);
DEBUG("%5d %s constructors (preinit_array) found at %p\n",
pid, si->name, si->preinit_array);
break;
case DT_PREINIT_ARRAYSZ:
si->preinit_array_count = ((unsigned)*d) / sizeof(Elf32_Addr);
break;
case DT_TEXTREL:
/* TODO: make use of this. */
/* this means that we might have to write into where the text
* segment was loaded during relocation... Do something with
* it.
*/
DEBUG("%5d Text segment should be writable during relocation.\n",
pid);
break;
}
}
DEBUG("%5d si->base = 0x%08x, si->strtab = %p, si->symtab = %p\n",
pid, si->base, si->strtab, si->symtab);
if((si->strtab == 0) || (si->symtab == 0)) {
DL_ERR("%5d missing essential tables", pid);
goto fail;
}
/* if this is the main executable, then load all of the preloads now */
if(si->flags & FLAG_EXE) {
int i;
memset(preloads, 0, sizeof(preloads));
for(i = 0; ldpreload_names[i] != NULL; i++) {
soinfo *lsi = find_library(ldpreload_names[i]);
if(lsi == 0) {
strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf));
DL_ERR("%5d could not load needed library '%s' for '%s' (%s)",
pid, ldpreload_names[i], si->name, tmp_err_buf);
goto fail;
}
lsi->refcount++;
preloads[i] = lsi;
}
}
for(d = si->dynamic; *d; d += 2) {
if(d[0] == DT_NEEDED){
DEBUG("%5d %s needs %s\n", pid, si->name, si->strtab + d[1]);
soinfo *lsi = find_library(si->strtab + d[1]);
if(lsi == 0) {
strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf));
DL_ERR("%5d could not load needed library '%s' for '%s' (%s)",
pid, si->strtab + d[1], si->name, tmp_err_buf);
goto fail;
}
/* Save the soinfo of the loaded DT_NEEDED library in the payload
of the DT_NEEDED entry itself, so that we can retrieve the
soinfo directly later from the dynamic segment. This is a hack,
but it allows us to map from DT_NEEDED to soinfo efficiently
later on when we resolve relocations, trying to look up a symbol
with dlsym().
*/
d[1] = (unsigned)lsi;
lsi->refcount++;
}
}
if(si->plt_rel) {
DEBUG("[ %5d relocating %s plt ]\n", pid, si->name );
if(soinfo_relocate(si, si->plt_rel, si->plt_rel_count))
goto fail;
}
if(si->rel) {
DEBUG("[ %5d relocating %s ]\n", pid, si->name );
if(soinfo_relocate(si, si->rel, si->rel_count))
goto fail;
}
si->flags |= FLAG_LINKED;
DEBUG("[ %5d finished linking %s ]\n", pid, si->name);
/* 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("%5d Can't protect segments for %s: %s",
pid, si->name, strerror(errno));
goto fail;
}
/* We can also turn on GNU RELRO protection */
if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) {
DL_ERR("%5d Can't enable GNU RELRO protection for %s: %s",
pid, si->name, strerror(errno));
goto fail;
}
/* If this is a SET?ID program, dup /dev/null to opened stdin,
stdout and stderr to close a security hole described in:
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc
*/
if (program_is_setuid)
nullify_closed_stdio ();
notify_gdb_of_load(si);
return 0;
fail:
ERROR("failed to link %s\n", si->name);
si->flags |= FLAG_ERROR;
return -1;
}
static void parse_library_path(const char *path, char *delim)
{
size_t len;
char *ldpaths_bufp = ldpaths_buf;
int i = 0;
len = strlcpy(ldpaths_buf, path, sizeof(ldpaths_buf));
while (i < LDPATH_MAX && (ldpaths[i] = strsep(&ldpaths_bufp, delim))) {
if (*ldpaths[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. not originally a delim). */
if (i > 0 && len >= sizeof(ldpaths_buf) &&
ldpaths_buf[sizeof(ldpaths_buf) - 2] != '\0') {
ldpaths[i - 1] = NULL;
} else {
ldpaths[i] = NULL;
}
}
static void parse_preloads(const char *path, char *delim)
{
size_t len;
char *ldpreloads_bufp = ldpreloads_buf;
int i = 0;
len = strlcpy(ldpreloads_buf, path, sizeof(ldpreloads_buf));
while (i < LDPRELOAD_MAX && (ldpreload_names[i] = strsep(&ldpreloads_bufp, delim))) {
if (*ldpreload_names[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. not originally a delim). */
if (i > 0 && len >= sizeof(ldpreloads_buf) &&
ldpreloads_buf[sizeof(ldpreloads_buf) - 2] != '\0') {
ldpreload_names[i - 1] = NULL;
} else {
ldpreload_names[i] = NULL;
}
}
/*
* 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 unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linker_base)
{
static soinfo linker_soinfo;
int argc = (int) *elfdata;
char **argv = (char**) (elfdata + 1);
unsigned *vecs = (unsigned*) (argv + argc + 1);
unsigned *v;
soinfo *si;
struct link_map * map;
const char *ldpath_env = NULL;
const char *ldpreload_env = NULL;
/* NOTE: we store the elfdata 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(elfdata);
pid = getpid();
#if TIMING
struct timeval t0, t1;
gettimeofday(&t0, 0);
#endif
/* Initialize environment functions, and get to the ELF aux vectors table */
vecs = linker_env_init(vecs);
/* Check auxv for AT_SECURE first to see if program is setuid, setgid,
has file caps, or caused a SELinux/AppArmor domain transition. */
for (v = vecs; v[0]; v += 2) {
if (v[0] == AT_SECURE) {
/* kernel told us whether to enable secure mode */
program_is_setuid = v[1];
goto sanitize;
}
}
/* Kernel did not provide AT_SECURE - fall back on legacy test. */
program_is_setuid = (getuid() != geteuid()) || (getgid() != getegid());
sanitize:
/* Sanitize environment if we're loading a setuid program */
if (program_is_setuid)
linker_env_secure();
debugger_init();
/* Get a few environment variables */
{
#if LINKER_DEBUG
const char* env;
env = linker_env_get("DEBUG"); /* XXX: TODO: Change to LD_DEBUG */
if (env)
debug_verbosity = atoi(env);
#endif
/* Normally, these are cleaned by linker_env_secure, but the test
* against program_is_setuid doesn't cost us anything */
if (!program_is_setuid) {
ldpath_env = linker_env_get("LD_LIBRARY_PATH");
ldpreload_env = linker_env_get("LD_PRELOAD");
}
}
INFO("[ android linker & debugger ]\n");
DEBUG("%5d elfdata @ 0x%08x\n", pid, (unsigned)elfdata);
si = soinfo_alloc(argv[0]);
if(si == 0) {
exit(-1);
}
/* bootstrap the link map, the main exe always needs to be first */
si->flags |= FLAG_EXE;
map = &(si->linkmap);
map->l_addr = 0;
map->l_name = 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.
*/
strlcpy((char*) linker_soinfo.name, "/system/bin/linker", sizeof linker_soinfo.name);
linker_soinfo.flags = 0;
linker_soinfo.base = linker_base;
insert_soinfo_into_debug_map(&linker_soinfo);
/* extract information passed from the kernel */
while(vecs[0] != 0){
switch(vecs[0]){
case AT_PHDR:
si->phdr = (Elf32_Phdr*) vecs[1];
break;
case AT_PHNUM:
si->phnum = (int) vecs[1];
break;
case AT_ENTRY:
si->entry = vecs[1];
break;
}
vecs += 2;
}
/* 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)
*/
int nn;
si->base = 0;
si->size = phdr_table_get_load_size(si->phdr, si->phnum);
si->load_bias = 0;
for ( nn = 0; nn < si->phnum; nn++ ) {
if (si->phdr[nn].p_type == PT_PHDR) {
si->load_bias = (Elf32_Addr)si->phdr - si->phdr[nn].p_vaddr;
si->base = (Elf32_Addr) si->phdr - si->phdr[nn].p_offset;
break;
}
}
si->dynamic = (unsigned *)-1;
si->refcount = 1;
/* Use LD_LIBRARY_PATH if we aren't setuid/setgid */
if (ldpath_env)
parse_library_path(ldpath_env, ":");
if (ldpreload_env) {
parse_preloads(ldpreload_env, " :");
}
if(soinfo_link_image(si, 0)) {
char errmsg[] = "CANNOT LINK EXECUTABLE\n";
write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf));
write(2, errmsg, sizeof(errmsg));
exit(-1);
}
soinfo_call_constructors(si);
#if ALLOW_SYMBOLS_FROM_MAIN
/* Set somain after we've loaded all the libraries in order to prevent
* linking of symbols back to the main image, which is not set up at that
* point yet.
*/
somain = si;
#endif
#if TIMING
gettimeofday(&t1,NULL);
PRINT("LINKER TIME: %s: %d microseconds\n", 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\n", argv[0],
linker_stats.reloc[RELOC_ABSOLUTE],
linker_stats.reloc[RELOC_RELATIVE],
linker_stats.reloc[RELOC_COPY],
linker_stats.reloc[RELOC_SYMBOL]);
#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)\n", argv[0], count, count * 4);
}
#endif
#if TIMING || STATS || COUNT_PAGES
fflush(stdout);
#endif
TRACE("[ %5d Ready to execute '%s' @ 0x%08x ]\n", pid, si->name,
si->entry);
return si->entry;
}
/*
* Find the value of AT_BASE passed to us by the kernel. This is the load
* location of the linker.
*/
static unsigned find_linker_base(unsigned **elfdata) {
int argc = (int) *elfdata;
char **argv = (char**) (elfdata + 1);
unsigned *vecs = (unsigned*) (argv + argc + 1);
while (vecs[0] != 0) {
vecs++;
}
/* The end of the environment block is marked by two NULL pointers */
vecs++;
while(vecs[0]) {
if (vecs[0] == AT_BASE) {
return vecs[1];
}
vecs += 2;
}
return 0; // should never happen
}
/* 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;
const Elf32_Phdr* phdr;
for (phdr = phdr_table; phdr < phdr_end; phdr++) {
if (phdr->p_type == PT_LOAD) {
return (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.
*/
unsigned __linker_init(unsigned **elfdata) {
unsigned linker_addr = find_linker_base(elfdata);
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 = (unsigned *) -1;
linker_so.phdr = phdr;
linker_so.phnum = elf_hdr->e_phnum;
linker_so.flags |= FLAG_LINKER;
if (soinfo_link_image(&linker_so, 0)) {
// 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(-1);
}
// We have successfully fixed our own relocations. It's safe to run
// the main part of the linker now.
return __linker_init_post_relocation(elfdata, linker_addr);
}
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