2 * Copyright (C) 2016 The Android Open Source Project
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * * Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in
12 * the documentation and/or other materials provided with the
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 #include "linker_main.h"
31 #include "linker_debug.h"
32 #include "linker_cfi.h"
33 #include "linker_gdb_support.h"
34 #include "linker_globals.h"
35 #include "linker_phdr.h"
36 #include "linker_utils.h"
38 #include "private/bionic_globals.h"
39 #include "private/bionic_tls.h"
40 #include "private/KernelArgumentBlock.h"
42 #include "android-base/strings.h"
43 #include "android-base/stringprintf.h"
45 #include "debuggerd/handler.h"
48 #include <async_safe/log.h>
52 extern void __libc_init_globals(KernelArgumentBlock&);
53 extern void __libc_init_AT_SECURE(KernelArgumentBlock&);
55 extern "C" void _start();
57 static ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf);
59 // These should be preserved static to avoid emitting
60 // RELATIVE relocations for the part of the code running
61 // before linker links itself.
63 // TODO (dimtiry): remove somain, rename solist to solist_head
64 static soinfo* solist;
65 static soinfo* sonext;
66 static soinfo* somain; // main process, always the one after libdl_info
68 void solist_add_soinfo(soinfo* si) {
73 bool solist_remove_soinfo(soinfo* si) {
74 soinfo *prev = nullptr, *trav;
75 for (trav = solist; trav != nullptr; trav = trav->next) {
82 if (trav == nullptr) {
83 // si was not in solist
84 PRINT("name \"%s\"@%p is not in solist!", si->get_realpath(), si);
88 // prev will never be null, because the first entry in solist is
89 // always the static libdl_info.
90 prev->next = si->next;
98 soinfo* solist_get_head() {
102 soinfo* solist_get_somain() {
106 int g_ld_debug_verbosity;
107 abort_msg_t* g_abort_message = nullptr; // For debuggerd.
109 static std::vector<std::string> g_ld_preload_names;
111 static std::vector<soinfo*> g_ld_preloads;
113 static void parse_path(const char* path, const char* delimiters,
114 std::vector<std::string>* resolved_paths) {
115 std::vector<std::string> paths;
116 split_path(path, delimiters, &paths);
117 resolve_paths(paths, resolved_paths);
120 static void parse_LD_LIBRARY_PATH(const char* path) {
121 std::vector<std::string> ld_libary_paths;
122 parse_path(path, ":", &ld_libary_paths);
123 g_default_namespace.set_ld_library_paths(std::move(ld_libary_paths));
126 static void parse_LD_PRELOAD(const char* path) {
127 g_ld_preload_names.clear();
128 if (path != nullptr) {
129 // We have historically supported ':' as well as ' ' in LD_PRELOAD.
130 g_ld_preload_names = android::base::Split(path, " :");
131 std::remove_if(g_ld_preload_names.begin(),
132 g_ld_preload_names.end(),
133 [] (const std::string& s) { return s.empty(); });
137 // An empty list of soinfos
138 static soinfo_list_t g_empty_list;
140 static void add_vdso(KernelArgumentBlock& args __unused) {
141 #if defined(AT_SYSINFO_EHDR)
142 ElfW(Ehdr)* ehdr_vdso = reinterpret_cast<ElfW(Ehdr)*>(args.getauxval(AT_SYSINFO_EHDR));
143 if (ehdr_vdso == nullptr) {
147 soinfo* si = soinfo_alloc(&g_default_namespace, "[vdso]", nullptr, 0, 0);
149 si->phdr = reinterpret_cast<ElfW(Phdr)*>(reinterpret_cast<char*>(ehdr_vdso) + ehdr_vdso->e_phoff);
150 si->phnum = ehdr_vdso->e_phnum;
151 si->base = reinterpret_cast<ElfW(Addr)>(ehdr_vdso);
152 si->size = phdr_table_get_load_size(si->phdr, si->phnum);
153 si->load_bias = get_elf_exec_load_bias(ehdr_vdso);
156 si->link_image(g_empty_list, soinfo_list_t::make_list(si), nullptr);
160 /* gdb expects the linker to be in the debug shared object list.
161 * Without this, gdb has trouble locating the linker's ".text"
162 * and ".plt" sections. Gdb could also potentially use this to
163 * relocate the offset of our exported 'rtld_db_dlactivity' symbol.
164 * Note that the linker shouldn't be on the soinfo list.
166 static link_map linker_link_map;
168 static void init_linker_info_for_gdb(ElfW(Addr) linker_base, char* linker_path) {
169 linker_link_map.l_addr = linker_base;
170 linker_link_map.l_name = linker_path;
173 * Set the dynamic field in the link map otherwise gdb will complain with
175 * warning: .dynamic section for "/system/bin/linker" is not at the
176 * expected address (wrong library or version mismatch?)
178 ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(linker_base);
179 ElfW(Phdr)* phdr = reinterpret_cast<ElfW(Phdr)*>(linker_base + elf_hdr->e_phoff);
180 phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base,
181 &linker_link_map.l_ld, nullptr);
185 extern "C" int __system_properties_init(void);
187 static const char* get_executable_path() {
188 static std::string executable_path;
189 if (executable_path.empty()) {
191 ssize_t path_len = readlink("/proc/self/exe", path, sizeof(path));
192 if (path_len == -1 || path_len >= static_cast<ssize_t>(sizeof(path))) {
193 async_safe_fatal("readlink('/proc/self/exe') failed: %s", strerror(errno));
195 executable_path = std::string(path, path_len);
198 return executable_path.c_str();
201 #if defined(__LP64__)
202 static char kLinkerPath[] = "/system/bin/linker64";
204 static char kLinkerPath[] = "/system/bin/linker";
208 * This code is called after the linker has linked itself and
209 * fixed it's own GOT. It is safe to make references to externs
210 * and other non-local data at this point.
212 static ElfW(Addr) __linker_init_post_relocation(KernelArgumentBlock& args) {
213 ProtectedDataGuard guard;
216 struct timeval t0, t1;
217 gettimeofday(&t0, 0);
220 // Sanitize the environment.
221 __libc_init_AT_SECURE(args);
223 // Initialize system properties
224 __system_properties_init(); // may use 'environ'
226 // Register the debuggerd signal handler.
228 debuggerd_callbacks_t callbacks = {
229 .get_abort_message = []() {
230 return g_abort_message;
232 .post_dump = ¬ify_gdb_of_libraries,
234 debuggerd_init(&callbacks);
237 g_linker_logger.ResetState();
239 // Get a few environment variables.
240 const char* LD_DEBUG = getenv("LD_DEBUG");
241 if (LD_DEBUG != nullptr) {
242 g_ld_debug_verbosity = atoi(LD_DEBUG);
245 #if defined(__LP64__)
246 INFO("[ Android dynamic linker (64-bit) ]");
248 INFO("[ Android dynamic linker (32-bit) ]");
251 // These should have been sanitized by __libc_init_AT_SECURE, but the test
252 // doesn't cost us anything.
253 const char* ldpath_env = nullptr;
254 const char* ldpreload_env = nullptr;
255 if (!getauxval(AT_SECURE)) {
256 ldpath_env = getenv("LD_LIBRARY_PATH");
257 if (ldpath_env != nullptr) {
258 INFO("[ LD_LIBRARY_PATH set to \"%s\" ]", ldpath_env);
260 ldpreload_env = getenv("LD_PRELOAD");
261 if (ldpreload_env != nullptr) {
262 INFO("[ LD_PRELOAD set to \"%s\" ]", ldpreload_env);
266 struct stat file_stat;
267 // Stat "/proc/self/exe" instead of executable_path because
268 // the executable could be unlinked by this point and it should
269 // not cause a crash (see http://b/31084669)
270 if (TEMP_FAILURE_RETRY(stat("/proc/self/exe", &file_stat)) != 0) {
271 async_safe_fatal("unable to stat \"/proc/self/exe\": %s", strerror(errno));
274 const char* executable_path = get_executable_path();
275 soinfo* si = soinfo_alloc(&g_default_namespace, executable_path, &file_stat, 0, RTLD_GLOBAL);
277 async_safe_fatal("Couldn't allocate soinfo: out of memory?");
280 /* bootstrap the link map, the main exe always needs to be first */
281 si->set_main_executable();
282 link_map* map = &(si->link_map_head);
284 // Register the main executable and the linker upfront to have
285 // gdb aware of them before loading the rest of the dependency
288 map->l_name = const_cast<char*>(executable_path);
289 insert_link_map_into_debug_map(map);
290 insert_link_map_into_debug_map(&linker_link_map);
292 // Extract information passed from the kernel.
293 si->phdr = reinterpret_cast<ElfW(Phdr)*>(args.getauxval(AT_PHDR));
294 si->phnum = args.getauxval(AT_PHNUM);
296 /* Compute the value of si->base. We can't rely on the fact that
297 * the first entry is the PHDR because this will not be true
298 * for certain executables (e.g. some in the NDK unit test suite)
301 si->size = phdr_table_get_load_size(si->phdr, si->phnum);
303 for (size_t i = 0; i < si->phnum; ++i) {
304 if (si->phdr[i].p_type == PT_PHDR) {
305 si->load_bias = reinterpret_cast<ElfW(Addr)>(si->phdr) - si->phdr[i].p_vaddr;
306 si->base = reinterpret_cast<ElfW(Addr)>(si->phdr) - si->phdr[i].p_offset;
310 si->dynamic = nullptr;
312 ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(si->base);
314 // We haven't supported non-PIE since Lollipop for security reasons.
315 if (elf_hdr->e_type != ET_DYN) {
316 // We don't use __libc_fatal here because we don't want a tombstone: it's
317 // been several years now but we still find ourselves on app compatibility
318 // investigations because some app's trying to launch an executable that
319 // hasn't worked in at least three years, and we've "helpfully" dropped a
320 // tombstone for them. The tombstone never provided any detail relevant to
321 // fixing the problem anyway, and the utility of drawing extra attention
322 // to the problem is non-existent at this late date.
323 async_safe_format_fd(STDERR_FILENO,
324 "\"%s\": error: Android 5.0 and later only support "
325 "position-independent executables (-fPIE).\n",
330 // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid).
331 parse_LD_LIBRARY_PATH(ldpath_env);
332 parse_LD_PRELOAD(ldpreload_env);
336 init_default_namespace(executable_path);
338 if (!si->prelink_image()) {
339 async_safe_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", g_argv[0], linker_get_error_buffer());
342 // add somain to global group
343 si->set_dt_flags_1(si->get_dt_flags_1() | DF_1_GLOBAL);
345 // Load ld_preloads and dependencies.
346 std::vector<const char*> needed_library_name_list;
347 size_t ld_preloads_count = 0;
349 for (const auto& ld_preload_name : g_ld_preload_names) {
350 needed_library_name_list.push_back(ld_preload_name.c_str());
354 for_each_dt_needed(si, [&](const char* name) {
355 needed_library_name_list.push_back(name);
358 const char** needed_library_names = &needed_library_name_list[0];
359 size_t needed_libraries_count = needed_library_name_list.size();
361 if (needed_libraries_count > 0 &&
362 !find_libraries(&g_default_namespace,
364 needed_library_names,
365 needed_libraries_count,
371 true /* add_as_children */,
372 true /* search_linked_namespaces */)) {
373 async_safe_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", g_argv[0], linker_get_error_buffer());
374 } else if (needed_libraries_count == 0) {
375 if (!si->link_image(g_empty_list, soinfo_list_t::make_list(si), nullptr)) {
376 async_safe_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", g_argv[0], linker_get_error_buffer());
378 si->increment_ref_count();
383 if (!get_cfi_shadow()->InitialLinkDone(solist)) {
384 async_safe_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", g_argv[0], linker_get_error_buffer());
387 si->call_pre_init_constructors();
389 /* After the prelink_image, the si->load_bias is initialized.
390 * For so lib, the map->l_addr will be updated in notify_gdb_of_load.
391 * We need to update this value for so exe here. So Unwind_Backtrace
392 * for some arch like x86 could work correctly within so exe.
394 map->l_addr = si->load_bias;
395 si->call_constructors();
398 gettimeofday(&t1, nullptr);
399 PRINT("LINKER TIME: %s: %d microseconds", g_argv[0], (int) (
400 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) -
401 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec)));
404 PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", g_argv[0],
405 linker_stats.count[kRelocAbsolute],
406 linker_stats.count[kRelocRelative],
407 linker_stats.count[kRelocCopy],
408 linker_stats.count[kRelocSymbol]);
415 for (n = 0; n < 4096; n++) {
417 unsigned x = bitmask[n];
418 #if defined(__LP64__)
419 for (i = 0; i < 32; i++) {
421 for (i = 0; i < 8; i++) {
430 PRINT("PAGES MODIFIED: %s: %d (%dKB)", g_argv[0], count, count * 4);
434 #if TIMING || STATS || COUNT_PAGES
438 ElfW(Addr) entry = args.getauxval(AT_ENTRY);
439 TRACE("[ Ready to execute \"%s\" @ %p ]", si->get_realpath(), reinterpret_cast<void*>(entry));
443 /* Compute the load-bias of an existing executable. This shall only
444 * be used to compute the load bias of an executable or shared library
445 * that was loaded by the kernel itself.
448 * elf -> address of ELF header, assumed to be at the start of the file.
450 * load bias, i.e. add the value of any p_vaddr in the file to get
451 * the corresponding address in memory.
453 static ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf) {
454 ElfW(Addr) offset = elf->e_phoff;
455 const ElfW(Phdr)* phdr_table =
456 reinterpret_cast<const ElfW(Phdr)*>(reinterpret_cast<uintptr_t>(elf) + offset);
457 const ElfW(Phdr)* phdr_end = phdr_table + elf->e_phnum;
459 for (const ElfW(Phdr)* phdr = phdr_table; phdr < phdr_end; phdr++) {
460 if (phdr->p_type == PT_LOAD) {
461 return reinterpret_cast<ElfW(Addr)>(elf) + phdr->p_offset - phdr->p_vaddr;
467 static void __linker_cannot_link(const char* argv0) {
468 async_safe_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", argv0, linker_get_error_buffer());
472 * This is the entry point for the linker, called from begin.S. This
473 * method is responsible for fixing the linker's own relocations, and
474 * then calling __linker_init_post_relocation().
476 * Because this method is called before the linker has fixed it's own
477 * relocations, any attempt to reference an extern variable, extern
478 * function, or other GOT reference will generate a segfault.
480 extern "C" ElfW(Addr) __linker_init(void* raw_args) {
481 KernelArgumentBlock args(raw_args);
483 // AT_BASE is set to 0 in the case when linker is run by iself
484 // so in order to link the linker it needs to calcuate AT_BASE
485 // using information at hand. The trick below takes advantage
486 // of the fact that the value of linktime_addr before relocations
487 // are run is an offset and this can be used to calculate AT_BASE.
488 static uintptr_t linktime_addr = reinterpret_cast<uintptr_t>(&linktime_addr);
489 ElfW(Addr) linker_addr = reinterpret_cast<uintptr_t>(&linktime_addr) - linktime_addr;
491 ElfW(Addr) entry_point = args.getauxval(AT_ENTRY);
492 ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(linker_addr);
493 ElfW(Phdr)* phdr = reinterpret_cast<ElfW(Phdr)*>(linker_addr + elf_hdr->e_phoff);
495 soinfo linker_so(nullptr, nullptr, nullptr, 0, 0);
497 linker_so.base = linker_addr;
498 linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum);
499 linker_so.load_bias = get_elf_exec_load_bias(elf_hdr);
500 linker_so.dynamic = nullptr;
501 linker_so.phdr = phdr;
502 linker_so.phnum = elf_hdr->e_phnum;
503 linker_so.set_linker_flag();
505 // Prelink the linker so we can access linker globals.
506 if (!linker_so.prelink_image()) __linker_cannot_link(args.argv[0]);
508 // This might not be obvious... The reasons why we pass g_empty_list
509 // in place of local_group here are (1) we do not really need it, because
510 // linker is built with DT_SYMBOLIC and therefore relocates its symbols against
511 // itself without having to look into local_group and (2) allocators
512 // are not yet initialized, and therefore we cannot use linked_list.push_*
513 // functions at this point.
514 if (!linker_so.link_image(g_empty_list, g_empty_list, nullptr)) __linker_cannot_link(args.argv[0]);
516 #if defined(__i386__)
517 // On x86, we can't make system calls before this point.
518 // We can't move this up because this needs to assign to a global.
519 // Note that until we call __libc_init_main_thread below we have
520 // no TLS, so you shouldn't make a system call that can fail, because
521 // it will SEGV when it tries to set errno.
522 __libc_init_sysinfo(args);
525 // Initialize the main thread (including TLS, so system calls really work).
526 __libc_init_main_thread(args);
528 // We didn't protect the linker's RELRO pages in link_image because we
529 // couldn't make system calls on x86 at that point, but we can now...
530 if (!linker_so.protect_relro()) __linker_cannot_link(args.argv[0]);
532 // Initialize the linker's static libc's globals
533 __libc_init_globals(args);
535 // store argc/argv/envp to use them for calling constructors
540 // Initialize the linker's own global variables
541 linker_so.call_constructors();
543 // If the linker is not acting as PT_INTERP entry_point is equal to
544 // _start. Which means that the linker is running as an executable and
545 // already linked by PT_INTERP.
547 // This happens when user tries to run 'adb shell /system/bin/linker'
548 // see also https://code.google.com/p/android/issues/detail?id=63174
549 if (reinterpret_cast<ElfW(Addr)>(&_start) == entry_point) {
550 async_safe_format_fd(STDOUT_FILENO,
551 "This is %s, the helper program for dynamic executables.\n",
556 init_linker_info_for_gdb(linker_addr, kLinkerPath);
558 // Initialize static variables. Note that in order to
559 // get correct libdl_info we need to call constructors
560 // before get_libdl_info().
561 sonext = solist = get_libdl_info(kLinkerPath, linker_link_map);
562 g_default_namespace.add_soinfo(solist);
564 // We have successfully fixed our own relocations. It's safe to run
565 // the main part of the linker now.
566 args.abort_message_ptr = &g_abort_message;
567 ElfW(Addr) start_address = __linker_init_post_relocation(args);
569 INFO("[ Jumping to _start (%p)... ]", reinterpret_cast<void*>(start_address));
571 // Return the address that the calling assembly stub should jump to.
572 return start_address;