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 if (__pthread_internal_remap_stack_with_mte()) {
65 async_safe_format_log(ANDROID_LOG_DEBUG, "libc", "remapped stacks as PROT_MTE");
66 }
67 }
68
69 // Use an initializer so __libc_sysinfo will have a fallback implementation
70 // while .preinit_array constructors run.
71 #if defined(__i386__)
72 __LIBC_HIDDEN__ void* __libc_sysinfo = reinterpret_cast<void*>(__libc_int0x80);
73 #endif
74
75 extern "C" __attribute__((weak)) void __hwasan_library_loaded(ElfW(Addr) base,
76 const ElfW(Phdr)* phdr,
77 ElfW(Half) phnum);
78 extern "C" __attribute__((weak)) void __hwasan_library_unloaded(ElfW(Addr) base,
79 const ElfW(Phdr)* phdr,
80 ElfW(Half) phnum);
81
82 // We need a helper function for __libc_preinit because compiling with LTO may
83 // inline functions requiring a stack protector check, but __stack_chk_guard is
84 // not initialized at the start of __libc_preinit. __libc_preinit_impl will run
85 // after __stack_chk_guard is initialized and therefore can safely have a stack
86 // protector.
87 __attribute__((noinline))
__libc_preinit_impl()88 static void __libc_preinit_impl() {
89 #if defined(__i386__)
90 __libc_init_sysinfo();
91 #endif
92
93 // Register libc.so's copy of the TLS generation variable so the linker can
94 // update it when it loads or unloads a shared object.
95 TlsModules& tls_modules = __libc_shared_globals()->tls_modules;
96 tls_modules.generation_libc_so = &__libc_tls_generation_copy;
97 __libc_tls_generation_copy = tls_modules.generation;
98
99 __libc_init_globals();
100 __libc_init_common();
101 __libc_init_scudo();
102
103 #if __has_feature(hwaddress_sanitizer)
104 // Notify the HWASan runtime library whenever a library is loaded or unloaded
105 // so that it can update its shadow memory.
106 // This has to happen before _libc_init_malloc which might dlopen to load
107 // profiler libraries.
108 __libc_shared_globals()->load_hook = __hwasan_library_loaded;
109 __libc_shared_globals()->unload_hook = __hwasan_library_unloaded;
110 #endif
111
112 // Hooks for various libraries to let them know that we're starting up.
113 __libc_globals.mutate(__libc_init_malloc);
114
115 // Install reserved signal handlers for assisting the platform's profilers.
116 __libc_init_profiling_handlers();
117
118 __libc_init_fork_handler();
119
120 __libc_shared_globals()->set_target_sdk_version_hook = __libc_set_target_sdk_version;
121
122 netdClientInit();
123 }
124
125 // We flag the __libc_preinit function as a constructor to ensure that
126 // its address is listed in libc.so's .init_array section.
127 // This ensures that the function is called by the dynamic linker as
128 // soon as the shared library is loaded.
129 // We give this constructor priority 1 because we want libc's constructor
130 // to run before any others (such as the jemalloc constructor), and lower
131 // is better (http://b/68046352).
__libc_preinit()132 __attribute__((constructor(1))) static void __libc_preinit() {
133 // The linker has initialized its copy of the global stack_chk_guard, and filled in the main
134 // thread's TLS slot with that value. Initialize the local global stack guard with its value.
135 __stack_chk_guard = reinterpret_cast<uintptr_t>(__get_tls()[TLS_SLOT_STACK_GUARD]);
136
137 __libc_preinit_impl();
138 }
139
140 // This function is called from the executable's _start entry point
141 // (see arch-$ARCH/bionic/crtbegin.c), which is itself called by the dynamic
142 // linker after it has loaded all shared libraries the executable depends on.
143 //
144 // Note that the dynamic linker has also run all constructors in the
145 // executable at this point.
__libc_init(void * raw_args,void (* onexit)(void)__unused,int (* slingshot)(int,char **,char **),structors_array_t const * const structors)146 __noreturn void __libc_init(void* raw_args,
147 void (*onexit)(void) __unused,
148 int (*slingshot)(int, char**, char**),
149 structors_array_t const * const structors) {
150 BIONIC_STOP_UNWIND;
151
152 KernelArgumentBlock args(raw_args);
153
154 // Several Linux ABIs don't pass the onexit pointer, and the ones that
155 // do never use it. Therefore, we ignore it.
156
157 // The executable may have its own destructors listed in its .fini_array
158 // so we need to ensure that these are called when the program exits
159 // normally.
160 if (structors->fini_array) {
161 __cxa_atexit(__libc_fini,structors->fini_array,nullptr);
162 }
163
164 __libc_init_mte_late();
165
166 // This roundabout way is needed so we don't use the static libc linked into the linker, which
167 // will not affect the process.
168 __libc_shared_globals()->memtag_stack_dlopen_callback = memtag_stack_dlopen_callback;
169
170 exit(slingshot(args.argc - __libc_shared_globals()->initial_linker_arg_count,
171 args.argv + __libc_shared_globals()->initial_linker_arg_count,
172 args.envp));
173 }
174
175 extern "C" libc_shared_globals* __loader_shared_globals();
176
__libc_shared_globals()177 __LIBC_HIDDEN__ libc_shared_globals* __libc_shared_globals() {
178 return __loader_shared_globals();
179 }
180