1 /*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
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
13 * distribution.
14 *
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,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29 /*
30 * This source files provides two important functions for dynamic
31 * executables:
32 *
33 * - a C runtime initializer (__libc_preinit), which is called by
34 * the dynamic linker when libc.so is loaded. This happens before
35 * any other initializer (e.g. static C++ constructors in other
36 * shared libraries the program depends on).
37 *
38 * - a program launch function (__libc_init), which is called after
39 * all dynamic linking has been performed.
40 */
41
42 #include <elf.h>
43 #include <stddef.h>
44 #include <stdint.h>
45 #include <stdio.h>
46 #include <stdlib.h>
47 #include "bionic/pthread_internal.h"
48 #include "libc_init_common.h"
49
50 #include "private/bionic_defs.h"
51 #include "private/bionic_elf_tls.h"
52 #include "private/bionic_globals.h"
53 #include "platform/bionic/macros.h"
54 #include "private/bionic_ssp.h"
55 #include "private/bionic_tls.h"
56 #include "private/KernelArgumentBlock.h"
57
58 extern "C" {
59 extern void netdClientInit(void);
60 extern int __cxa_atexit(void (*)(void *), void *, void *);
61 };
62
memtag_stack_dlopen_callback()63 void memtag_stack_dlopen_callback() {
64 async_safe_format_log(ANDROID_LOG_DEBUG, "libc", "remapping stacks as PROT_MTE");
65 __pthread_internal_remap_stack_with_mte();
66 }
67
68 // Use an initializer so __libc_sysinfo will have a fallback implementation
69 // while .preinit_array constructors run.
70 #if defined(__i386__)
71 __LIBC_HIDDEN__ void* __libc_sysinfo = reinterpret_cast<void*>(__libc_int0x80);
72 #endif
73
74 extern "C" __attribute__((weak)) void __hwasan_library_loaded(ElfW(Addr) base,
75 const ElfW(Phdr)* phdr,
76 ElfW(Half) phnum);
77 extern "C" __attribute__((weak)) void __hwasan_library_unloaded(ElfW(Addr) base,
78 const ElfW(Phdr)* phdr,
79 ElfW(Half) phnum);
80
81 // We need a helper function for __libc_preinit because compiling with LTO may
82 // inline functions requiring a stack protector check, but __stack_chk_guard is
83 // not initialized at the start of __libc_preinit. __libc_preinit_impl will run
84 // after __stack_chk_guard is initialized and therefore can safely have a stack
85 // protector.
86 __attribute__((noinline))
__libc_preinit_impl()87 static void __libc_preinit_impl() {
88 #if defined(__i386__)
89 __libc_init_sysinfo();
90 #endif
91
92 // Register libc.so's copy of the TLS generation variable so the linker can
93 // update it when it loads or unloads a shared object.
94 TlsModules& tls_modules = __libc_shared_globals()->tls_modules;
95 tls_modules.generation_libc_so = &__libc_tls_generation_copy;
96 __libc_tls_generation_copy = tls_modules.generation;
97
98 __libc_init_globals();
99 __libc_init_common();
100 __libc_init_scudo();
101
102 #if __has_feature(hwaddress_sanitizer)
103 // Notify the HWASan runtime library whenever a library is loaded or unloaded
104 // so that it can update its shadow memory.
105 // This has to happen before _libc_init_malloc which might dlopen to load
106 // profiler libraries.
107 __libc_shared_globals()->load_hook = __hwasan_library_loaded;
108 __libc_shared_globals()->unload_hook = __hwasan_library_unloaded;
109 #endif
110
111 // Hooks for various libraries to let them know that we're starting up.
112 __libc_globals.mutate(__libc_init_malloc);
113
114 // Install reserved signal handlers for assisting the platform's profilers.
115 __libc_init_profiling_handlers();
116
117 __libc_init_fork_handler();
118
119 __libc_shared_globals()->set_target_sdk_version_hook = __libc_set_target_sdk_version;
120
121 netdClientInit();
122 }
123
124 // We flag the __libc_preinit function as a constructor to ensure that
125 // its address is listed in libc.so's .init_array section.
126 // This ensures that the function is called by the dynamic linker as
127 // soon as the shared library is loaded.
128 // We give this constructor priority 1 because we want libc's constructor
129 // to run before any others (such as the jemalloc constructor), and lower
130 // is better (http://b/68046352).
__libc_preinit()131 __attribute__((constructor(1))) static void __libc_preinit() {
132 // The linker has initialized its copy of the global stack_chk_guard, and filled in the main
133 // thread's TLS slot with that value. Initialize the local global stack guard with its value.
134 __stack_chk_guard = reinterpret_cast<uintptr_t>(__get_tls()[TLS_SLOT_STACK_GUARD]);
135
136 __libc_preinit_impl();
137 }
138
139 // This function is called from the executable's _start entry point
140 // (see arch-$ARCH/bionic/crtbegin.c), which is itself called by the dynamic
141 // linker after it has loaded all shared libraries the executable depends on.
142 //
143 // Note that the dynamic linker has also run all constructors in the
144 // executable at this point.
__libc_init(void * raw_args,void (* onexit)(void)__unused,int (* slingshot)(int,char **,char **),structors_array_t const * const structors)145 __noreturn void __libc_init(void* raw_args,
146 void (*onexit)(void) __unused,
147 int (*slingshot)(int, char**, char**),
148 structors_array_t const * const structors) {
149 BIONIC_STOP_UNWIND;
150
151 KernelArgumentBlock args(raw_args);
152
153 // Several Linux ABIs don't pass the onexit pointer, and the ones that
154 // do never use it. Therefore, we ignore it.
155
156 // The executable may have its own destructors listed in its .fini_array
157 // so we need to ensure that these are called when the program exits
158 // normally.
159 if (structors->fini_array) {
160 __cxa_atexit(__libc_fini,structors->fini_array,nullptr);
161 }
162
163 __libc_init_mte_late();
164
165 // This roundabout way is needed so we don't use the static libc linked into the linker, which
166 // will not affect the process.
167 __libc_shared_globals()->memtag_stack_dlopen_callback = memtag_stack_dlopen_callback;
168
169 exit(slingshot(args.argc - __libc_shared_globals()->initial_linker_arg_count,
170 args.argv + __libc_shared_globals()->initial_linker_arg_count,
171 args.envp));
172 }
173
174 extern "C" libc_shared_globals* __loader_shared_globals();
175
__libc_shared_globals()176 __LIBC_HIDDEN__ libc_shared_globals* __libc_shared_globals() {
177 return __loader_shared_globals();
178 }
179